diff --git a/scripts/tracker-seed/seed-tracker-items.mjs b/scripts/tracker-seed/seed-tracker-items.mjs
index 2b7da26..2def342 100644
--- a/scripts/tracker-seed/seed-tracker-items.mjs
+++ b/scripts/tracker-seed/seed-tracker-items.mjs
@@ -63,7 +63,8 @@ function mintToken() {
 }
 
 async function listTitles(token, productId) {
-  const url = `${API}/api/items?productId=${encodeURIComponent(productId)}&limit=500`;
+  // limit max is 100 (server caps it); 500 would 400 and silently break dedupe.
+  const url = `${API}/api/items?productId=${encodeURIComponent(productId)}&limit=100`;
   const res = await fetch(url, {
     headers: { authorization: `Bearer ${token}`, 'x-product-id': productId },
   });
@@ -72,6 +73,36 @@ async function listTitles(token, productId) {
   return new Set((data.items || []).map((i) => i.title));
 }
 
+/** Derive an uppercase-letters-only license prefix (<=8) from a productId. */
+function licensePrefix(productId) {
+  return productId.replace(/[^a-z]/gi, '').toUpperCase().slice(0, 8) || 'PRD';
+}
+
+/**
+ * Ensure a product exists before creating items under it. POST /items skips
+ * product validation when productId is in the body, but GET /items validates —
+ * so without registration the dedupe list 400s ("Unknown product") and
+ * re-runs create duplicates. Idempotent: treats 409/200/201 as success.
+ */
+async function ensureProduct(token, productId) {
+  const res = await fetch(`${API}/api/products`, {
+    method: 'POST',
+    headers: {
+      authorization: `Bearer ${token}`,
+      'content-type': 'application/json',
+      'x-product-id': productId,
+    },
+    body: JSON.stringify({
+      productId,
+      displayName: productId.charAt(0).toUpperCase() + productId.slice(1),
+      licensePrefix: licensePrefix(productId),
+    }),
+  });
+  if (!res.ok && res.status !== 409) {
+    console.warn(`  warn: register ${productId} -> HTTP ${res.status}`);
+  }
+}
+
 async function createItem(token, item) {
   const res = await fetch(`${API}/api/items`, {
     method: 'POST',
@@ -102,6 +133,13 @@ async function main() {
   }
 
   const token = mintToken();
+
+  // Register every referenced product first so the dedupe list (GET /items)
+  // doesn't 400 on unknown products — which would silently cause duplicates.
+  const productIds = [...new Set(items.map((it) => it.productId))];
+  console.log(`Ensuring ${productIds.length} product(s) are registered...`);
+  for (const pid of productIds) await ensureProduct(token, pid);
+
   const titleCache = new Map();
   let created = 0;
   let skipped = 0;
@@ -111,7 +149,13 @@ async function main() {
     try {
       if (!FORCE) {
         if (!titleCache.has(it.productId)) {
-          titleCache.set(it.productId, await listTitles(token, it.productId).catch(() => new Set()));
+          titleCache.set(
+            it.productId,
+            await listTitles(token, it.productId).catch((e) => {
+              console.warn(`  warn: dedupe list for ${it.productId} failed (${e.message}); may create duplicates`);
+              return new Set();
+            })
+          );
         }
         if (titleCache.get(it.productId).has(it.title)) {
           console.log(`  SKIP   ${it.productId.padEnd(16)} ${it.title} (already exists)`);