diff --git a/src/app/(app)/invoicing/page.tsx b/src/app/(app)/invoicing/page.tsx
index b8e89da..9018f5a 100644
--- a/src/app/(app)/invoicing/page.tsx
+++ b/src/app/(app)/invoicing/page.tsx
@@ -29,6 +29,7 @@ import {
   matchesSearch,
   resolveInvoicePdfUrl,
   resolveInvoiceLineDefaults,
+  surplusQty,
   type InvoiceLineOverride,
   type InvoicingRow,
 } from "./view-model";
@@ -837,6 +838,7 @@ function SingleOrderQbModal({
             const priceId = `invoice-price-${row.id}`;
             const included = includedRowIds.has(row.id);
             const label = itemLabel(row);
+            const surplus = surplusQty(row);
             return (
               <div
                 key={row.id}
@@ -875,7 +877,17 @@ function SingleOrderQbModal({
                   </div>
                 </div>
                 <label className="space-y-1 text-sm" htmlFor={qtyId}>
-                  <span>Qty</span>
+                  <span className="flex items-center justify-between gap-2">
+                    <span>Qty</span>
+                    {surplus > 0 ? (
+                      <span
+                        className="rounded-full border border-info/40 bg-info/10 px-1.5 py-0.5 text-[10px] font-semibold uppercase tracking-wide text-info"
+                        title={`Supplier delivered ${row.qtyCollected}, customer ordered ${row.orderQty}. ${surplus} goes to stock — book via /api/v1/stock/surplus-book.`}
+                      >
+                        +{surplus} to stock
+                      </span>
+                    ) : null}
+                  </span>
                   <input
                     id={qtyId}
                     type="number"
@@ -1093,6 +1105,7 @@ function SingleDeliveryNoteModal({
             const priceId = `dn-price-${row.id}`;
             const included = includedRowIds.has(row.id);
             const label = itemLabel(row);
+            const surplus = surplusQty(row);
             return (
               <div
                 key={row.id}
@@ -1131,7 +1144,17 @@ function SingleDeliveryNoteModal({
                   </div>
                 </div>
                 <label className="space-y-1 text-sm" htmlFor={qtyId}>
-                  <span>Qty</span>
+                  <span className="flex items-center justify-between gap-2">
+                    <span>Qty</span>
+                    {surplus > 0 ? (
+                      <span
+                        className="rounded-full border border-info/40 bg-info/10 px-1.5 py-0.5 text-[10px] font-semibold uppercase tracking-wide text-info"
+                        title={`Supplier delivered ${row.qtyCollected}, customer ordered ${row.orderQty}. ${surplus} will be booked to stock via /api/v1/stock/surplus-book after delivery.`}
+                      >
+                        +{surplus} to stock
+                      </span>
+                    ) : null}
+                  </span>
                   <input
                     id={qtyId}
                     type="number"
diff --git a/src/app/(app)/invoicing/view-model.test.ts b/src/app/(app)/invoicing/view-model.test.ts
index 0721661..9a95ead 100644
--- a/src/app/(app)/invoicing/view-model.test.ts
+++ b/src/app/(app)/invoicing/view-model.test.ts
@@ -14,7 +14,9 @@ import {
   isGroupReadyToPrint,
   matchesSearch,
   pickClosestCustomer,
+  resolveInvoiceLineDefaults,
   resolveInvoicePdfUrl,
+  surplusQty,
   type InvoicingRow,
   type InvoicingStatus,
 } from "./view-model";
@@ -474,3 +476,54 @@ describe("resolveInvoicePdfUrl", () => {
     })).toBe("https://pb.example.com/api/files/pbc_order_items/row-1/invoice_a.pdf");
   });
 });
+
+describe("resolveInvoiceLineDefaults", () => {
+  it("uses the customer order qty, not the supplier-collected qty (MOQ overflow scenario)", () => {
+    // Customer ordered 4, supplier MOQ forced an order of 10, supplier
+    // delivered all 10. The invoice must reflect 4 — only the customer
+    // qty goes on the QuickBooks payload. The remaining 6 is routed to
+    // stock via /api/v1/stock/surplus-book (see surplusQty below).
+    const row = makeRow({ orderQty: 4, qtyCollected: 10 });
+    expect(resolveInvoiceLineDefaults(row).qty).toBe(4);
+  });
+
+  it("falls back to qtyCollected when there is no customer orderQty (legacy rows)", () => {
+    const row = makeRow({ orderQty: null, qtyCollected: 6 });
+    expect(resolveInvoiceLineDefaults(row).qty).toBe(6);
+  });
+
+  it("defaults to 1 when neither qty is recorded", () => {
+    const row = makeRow({ orderQty: null, qtyCollected: null });
+    expect(resolveInvoiceLineDefaults(row).qty).toBe(1);
+  });
+
+  it("uses orderQty even when it equals qtyCollected (no overflow)", () => {
+    const row = makeRow({ orderQty: 4, qtyCollected: 4 });
+    expect(resolveInvoiceLineDefaults(row).qty).toBe(4);
+  });
+
+  it("uses orderQty when it exceeds qtyCollected (short delivery — never invoices the surplus)", () => {
+    const row = makeRow({ orderQty: 10, qtyCollected: 4 });
+    expect(resolveInvoiceLineDefaults(row).qty).toBe(10);
+  });
+});
+
+describe("surplusQty", () => {
+  it("returns the supplier-MOQ overflow (collected - ordered)", () => {
+    expect(surplusQty(makeRow({ orderQty: 4, qtyCollected: 10 }))).toBe(6);
+  });
+
+  it("returns 0 when collected equals ordered (no overflow)", () => {
+    expect(surplusQty(makeRow({ orderQty: 4, qtyCollected: 4 }))).toBe(0);
+  });
+
+  it("returns 0 when short delivery (collected < ordered)", () => {
+    expect(surplusQty(makeRow({ orderQty: 10, qtyCollected: 4 }))).toBe(0);
+  });
+
+  it("returns 0 when either side is missing", () => {
+    expect(surplusQty(makeRow({ orderQty: null, qtyCollected: 10 }))).toBe(0);
+    expect(surplusQty(makeRow({ orderQty: 4, qtyCollected: null }))).toBe(0);
+    expect(surplusQty(makeRow({ orderQty: null, qtyCollected: null }))).toBe(0);
+  });
+});
diff --git a/src/app/(app)/invoicing/view-model.ts b/src/app/(app)/invoicing/view-model.ts
index 7b599ee..4203e15 100644
--- a/src/app/(app)/invoicing/view-model.ts
+++ b/src/app/(app)/invoicing/view-model.ts
@@ -358,16 +358,36 @@ export type InvoiceLineOverride = {
 };
 
 export function resolveInvoiceLineDefaults(row: InvoicingRow): { qty: number; price: number } {
+  // The invoice qty must reflect what the CUSTOMER ordered (`orderQty`),
+  // never what was `qtyCollected` from the supplier. When a supplier
+  // MOQ forces us to buy more than the customer wanted (e.g. ordered 4,
+  // received 10), the operator routes the surplus into stock via
+  // /api/v1/stock/surplus-book — only the customer-facing 4 goes on the
+  // invoice / delivery note. Fall back to `qtyCollected` only when no
+  // explicit customer qty was ever recorded (legacy rows / quotes not
+  // yet promoted into a real order).
   const qty =
-    typeof row.qtyCollected === "number"
-      ? row.qtyCollected
-      : typeof row.orderQty === "number"
-        ? row.orderQty
+    typeof row.orderQty === "number"
+      ? row.orderQty
+      : typeof row.qtyCollected === "number"
+        ? row.qtyCollected
         : 1;
   const price = typeof row.sellingPrice === "number" ? row.sellingPrice : 0;
   return { qty, price };
 }
 
+/**
+ * How many units of `row` were collected from the supplier that do NOT
+ * belong on the customer's invoice — i.e. the supplier-MOQ overflow
+ * that should be booked into stock. Returns 0 when there's no
+ * headroom (collected ≤ ordered) or when either side is unknown.
+ */
+export function surplusQty(row: InvoicingRow): number {
+  if (typeof row.qtyCollected !== "number") return 0;
+  if (typeof row.orderQty !== "number") return 0;
+  return Math.max(0, row.qtyCollected - row.orderQty);
+}
+
 export function buildQbInvoicePayload(input: {
   orderNumber: string;
   billingCompany: string;
diff --git a/src/app/api/v1/delivery-notes/route.ts b/src/app/api/v1/delivery-notes/route.ts
index a000dcb..56e0eb9 100644
--- a/src/app/api/v1/delivery-notes/route.ts
+++ b/src/app/api/v1/delivery-notes/route.ts
@@ -123,10 +123,24 @@ export async function POST(req: NextRequest) {
     });
     return NextResponse.json(result, { status: 201 });
   } catch (err: unknown) {
-    const message =
-      err instanceof Error
-        ? err.message
-        : "Failed to create ad-hoc delivery note";
+    const e = err as {
+      message?: string;
+      response?: { data?: unknown; status?: number };
+      data?: unknown;
+    };
+    const pbDetail = e.response?.data ?? e.data;
+    const baseMessage =
+      err instanceof Error ? err.message : "Failed to create ad-hoc delivery note";
+    const message = pbDetail
+      ? `${baseMessage} | ${JSON.stringify(pbDetail).slice(0, 500)}`
+      : baseMessage;
+    console.error("[delivery-notes.create]", {
+      message: baseMessage,
+      pbDetail,
+      createdByProvided: !!createdBy,
+      customer: body.customer,
+      itemCount: body.items?.length,
+    });
     return NextResponse.json({ error: message }, { status: 500 });
   }
 }
diff --git a/src/lib/letterhead.ts b/src/lib/letterhead.ts
index 5f4b916..58ab356 100644
--- a/src/lib/letterhead.ts
+++ b/src/lib/letterhead.ts
@@ -6,15 +6,18 @@ import type { BaseRecord } from "./types";
 /**
  * Letterhead — server-side read model for a row in `letterhead_settings`.
  *
- * Each company (CNL, ISHERWOOD) has exactly one row (enforced by the
- * `idx_letterhead_settings_one_per_company` unique index). The PDF
- * generator fetches this row fresh on every render so edits in the
- * PB admin UI (logo swap, bank detail fix, terms tweak, accent color
- * change) propagate to the next quote without a code deploy.
+ * Each company / brand has exactly one row. The PDF generator fetches
+ * this row fresh on every render so edits in the PB admin UI (logo
+ * swap, bank detail fix, terms tweak, accent color change) propagate
+ * to the next quote / DN / PO without a code deploy.
  */
-export type LetterheadCode = "CNL" | "ISHERWOOD";
+export type LetterheadCode = "CNL" | "ISHERWOOD" | "WESTSCOTT GROUP OF COMPANIES";
 
-export const LETTERHEAD_CODES: readonly LetterheadCode[] = ["CNL", "ISHERWOOD"] as const;
+export const LETTERHEAD_CODES: readonly LetterheadCode[] = [
+  "CNL",
+  "ISHERWOOD",
+  "WESTSCOTT GROUP OF COMPANIES",
+] as const;
 
 /**
  * Pick the letterhead code that matches a given company name. The
diff --git a/src/lib/server/delivery-notes-service.ts b/src/lib/server/delivery-notes-service.ts
index 28c3fa9..b860e88 100644
--- a/src/lib/server/delivery-notes-service.ts
+++ b/src/lib/server/delivery-notes-service.ts
@@ -38,7 +38,6 @@ import { renderDeliveryNotePdf } from "@/lib/pdf/render";
 import { resolveDeliveryNoteLineQty } from "@/lib/pdf/delivery-note-document";
 import {
   fetchLetterhead,
-  letterheadForCompany,
   loadLetterheadLogoDataUri,
 } from "@/lib/letterhead";
 import type {
@@ -59,6 +58,33 @@ const COMPANIES = "companies";
 const SUPPLIERS = "suppliers";
 const ORDERS = "orders";
 
+/**
+ * The letterhead every delivery-note PDF renders under.
+ *
+ * Hardcoded by business decision: the Westcott group owns
+ * multiple subsidiaries (CNL, ISHERWOOD, Test Engineering,
+ * etc.) but the printed DN is a Westcott-Group-branded
+ * document regardless of which subsidiary the customer
+ * belongs to. The actual letterhead content (logo, address,
+ * banking, accent colour) lives in `letterhead_settings` —
+ * this constant is the *lookup* into that table, not the
+ * content itself.
+ *
+ * `fetchLetterhead` runs a case-insensitive substring match
+ * on `letterhead_settings.display_name` against this value,
+ * so the matching row in PB must have a display_name that
+ * contains this string (verbatim or as a substring). The row
+ * the user added in PB (id `5wezvypn6fy47p9`) has
+ * display_name `WESTSCOTT GROUP OF COMPANIES` which matches
+ * cleanly.
+ *
+ * If you want to swap the brand (e.g. rebrand to a new parent
+ * company), update the PB row and change this string in
+ * lockstep. The PDF will pick up the new content from PB
+ * automatically without any code change beyond the constant.
+ */
+const DELIVERY_NOTE_LETTERHEAD_CODE = "WESTSCOTT GROUP OF COMPANIES";
+
 /**
  * Lifecycle transitions for the delivery_notes.status field. The
  * service methods enforce these — they reject any transition that
@@ -345,7 +371,13 @@ async function attachDeliveryNoteToQuote(
   } else {
     // Path 2: re-render the unsigned PDF from the order items.
     const companyName = dn.expand?.company?.company ?? "";
-    const letterheadCode = letterheadForCompany(companyName) ?? "CNL";
+    // All delivery-note PDFs render under the Westcott
+    // Group letterhead, regardless of which subsidiary the
+    // customer belongs to — see DELIVERY_NOTE_LETTERHEAD_CODE.
+    // The `companyName` above still goes into the PDF meta
+    // block so the printed document tells the driver which
+    // subsidiary the delivery is for.
+    const letterheadCode = DELIVERY_NOTE_LETTERHEAD_CODE;
     const letterhead = await fetchLetterhead(letterheadCode);
     const logoDataUri = await loadLetterheadLogoDataUri(letterheadCode);
     const customerName = dn.expand?.customer?.customer ?? "";
@@ -813,7 +845,7 @@ export async function createAdHocDeliveryNote(
         ? (companyRow as unknown as { company: string }).company
         : "";
 
-    const letterheadCode = letterheadForCompany(companyName) ?? "CNL";
+    const letterheadCode = DELIVERY_NOTE_LETTERHEAD_CODE;
     const letterhead = await fetchLetterhead(letterheadCode);
     const logoDataUri = await loadLetterheadLogoDataUri(letterheadCode);
 
@@ -932,7 +964,13 @@ export async function regenerateDeliveryNotePdf(
     (await resolveRelationName(pb, dn.company, COMPANIES, "company")) ??
     "";
 
-  const letterheadCode = letterheadForCompany(companyName) ?? "CNL";
+  // All delivery-note PDFs render under the Westcott
+  // Group letterhead, regardless of which subsidiary the
+  // customer belongs to — see DELIVERY_NOTE_LETTERHEAD_CODE.
+  // The `companyName` above still goes into the PDF meta
+  // block so the printed document tells the driver which
+  // subsidiary the delivery is for.
+  const letterheadCode = DELIVERY_NOTE_LETTERHEAD_CODE;
   const [letterhead, logoDataUri] = await Promise.all([
     fetchLetterhead(letterheadCode),
     loadLetterheadLogoDataUri(letterheadCode),