diff --git a/scripts/diagnose-sync.ts b/scripts/diagnose-sync.ts
new file mode 100644
index 0000000..f7dd6bf
--- /dev/null
+++ b/scripts/diagnose-sync.ts
@@ -0,0 +1,93 @@
+/// <reference lib="deno.ns" />
+// Answers "did SimpleFIN send it, or did we drop it?" from the raw archive.
+//
+// Usage:
+//   deno run -A scripts/diagnose-sync.ts [path-to-quantum.db]
+//
+// Against a deployed container, copy the file out first:
+//   podman cp <container>:/data/quantum.db ./quantum.db
+//   deno run -A scripts/diagnose-sync.ts ./quantum.db
+
+import { DatabaseSync } from 'node:sqlite';
+
+const path = Deno.args[0] ?? './data/quantum.db';
+const db = new DatabaseSync(path);
+
+const fmtDate = (unix: number | null) =>
+	unix ? new Date(unix * 1000).toISOString().slice(0, 10) : '—';
+
+console.log(`\n=== Sync attempts (latest 5) ===`);
+const syncs = db
+	.prepare(
+		`SELECT id, fetched_at, ok, error, LENGTH(payload) AS bytes
+		 FROM raw_syncs ORDER BY id DESC LIMIT 5`
+	)
+	.all() as Record<string, unknown>[];
+for (const s of syncs) {
+	console.log(
+		`#${s.id}  ${s.fetched_at}  ${s.ok ? 'ok' : 'FAILED'}  ${s.bytes ?? 0} bytes${s.error ? `  error: ${s.error}` : ''}`
+	);
+}
+
+const latest = db
+	.prepare('SELECT id, fetched_at, payload FROM raw_syncs WHERE ok = 1 ORDER BY id DESC LIMIT 1')
+	.get() as { id: number; fetched_at: string; payload: string } | undefined;
+
+if (!latest?.payload) {
+	console.log('\nNo successful sync payload archived yet — nothing to compare.');
+	Deno.exit(0);
+}
+
+console.log(`\n=== Latest successful payload (raw_syncs #${latest.id}, ${latest.fetched_at}) ===`);
+const parsed = JSON.parse(latest.payload) as {
+	errors?: unknown[];
+	accounts?: Record<string, unknown>[];
+};
+
+if (parsed.errors?.length) {
+	console.log(`Connection errors reported by the Bridge:`);
+	for (const e of parsed.errors) console.log(`  ! ${e}`);
+} else {
+	console.log('No connection errors in payload.');
+}
+
+console.log('\nWhat the Bridge sent, per account:');
+for (const account of parsed.accounts ?? []) {
+	const txns = (account.transactions ?? []) as Record<string, unknown>[];
+	const posted = txns
+		.map((t) => (typeof t.posted === 'number' ? t.posted : null))
+		.filter((p): p is number => p != null && p > 0);
+	const range = posted.length
+		? `${fmtDate(Math.min(...posted))} … ${fmtDate(Math.max(...posted))}`
+		: 'no posted dates';
+	console.log(
+		`  ${String(account.id).padEnd(28)} ${String(account.name).padEnd(24)} ` +
+			`${String(txns.length).padStart(4)} txns in payload  (${range})`
+	);
+}
+
+console.log('\nWhat Quantum has normalized, per account:');
+const rows = db
+	.prepare(
+		`SELECT a.id, COALESCE(a.display_name, a.name) AS name, a.state,
+		        COUNT(t.id) AS n, MIN(t.posted) AS min_posted, MAX(t.posted) AS max_posted
+		 FROM accounts a LEFT JOIN transactions t ON t.account_id = a.id AND t.removed_at IS NULL
+		 GROUP BY a.id ORDER BY a.id`
+	)
+	.all() as Record<string, unknown>[];
+for (const r of rows) {
+	console.log(
+		`  ${String(r.id).padEnd(28)} ${String(r.name).padEnd(24)} ` +
+			`${String(r.n).padStart(4)} txns in db       ` +
+			`(${fmtDate(r.min_posted as number | null)} … ${fmtDate(r.max_posted as number | null)})  [${r.state}]`
+	);
+}
+
+console.log(`\nReading the result:
+  - Account has txns in payload but 0 in db  -> Quantum bug; please report.
+  - Account has 0 txns in payload            -> the provider isn't delivering
+    transactions for that institution (common for investment/savings accounts
+    via some aggregators). Check the connection at SimpleFIN Bridge.
+  - FAILED sync rows with a normalization error -> a malformed amount or
+    payload; the error text says which.`);
+db.close();
diff --git a/src/lib/server/services/normalize.test.ts b/src/lib/server/services/normalize.test.ts
index d50c044..90c0b18 100644
--- a/src/lib/server/services/normalize.test.ts
+++ b/src/lib/server/services/normalize.test.ts
@@ -15,13 +15,20 @@ Deno.test('parseAmountToCents handles SimpleFIN decimal strings exactly', () =>
 	assertEq(parseAmountToCents('1.005'), 101, 'rounds half away from zero');
 	assertEq(parseAmountToCents('-1.005'), -101);
 	assertEq(parseAmountToCents('4222.19'), 422219, 'no float drift');
-	let threw = false;
-	try {
-		parseAmountToCents('12,34');
-	} catch {
-		threw = true;
+	// provider variance that must not fail a sync
+	assertEq(parseAmountToCents('+12.00'), 1200, 'explicit plus sign');
+	assertEq(parseAmountToCents('.50'), 50, 'bare leading dot');
+	assertEq(parseAmountToCents('-.50'), -50, 'negative bare dot');
+	assertEq(parseAmountToCents('1,234.56'), 123456, 'thousands separators');
+	for (const bad of ['', '.', 'abc', '12.34.56', '-']) {
+		let threw = false;
+		try {
+			parseAmountToCents(bad);
+		} catch {
+			threw = true;
+		}
+		if (!threw) throw new Error(`expected ${JSON.stringify(bad)} to throw`);
 	}
-	if (!threw) throw new Error('expected malformed amount to throw');
 });
 
 Deno.test('normalizePayload maps accounts, transactions, errors', () => {
diff --git a/src/lib/server/services/normalize.ts b/src/lib/server/services/normalize.ts
index dab0d26..e946184 100644
--- a/src/lib/server/services/normalize.ts
+++ b/src/lib/server/services/normalize.ts
@@ -38,15 +38,19 @@ export interface NormalizedPayload {
 /**
  * Parse a SimpleFIN decimal string into integer cents without floats.
  * Assumes 2-minor-unit currencies; extra fraction digits are rounded
- * (half away from zero).
+ * (half away from zero). Tolerates real-world provider variance: an
+ * explicit "+" sign, thousands separators ("1,234.56"), and a bare
+ * leading dot (".50") — one exotic amount must not fail a whole sync.
  */
 export function parseAmountToCents(amount: string | number): number {
-	const text = String(amount).trim();
-	const match = text.match(/^(-?)(\d+)(?:\.(\d+))?$/);
-	if (!match) throw new Error(`Unparseable amount: ${JSON.stringify(amount)}`);
-	const [, sign, whole, fracRaw = ''] = match;
+	const text = String(amount).trim().replace(/,/g, '');
+	const match = text.match(/^([+-]?)(\d*)(?:\.(\d+))?$/);
+	if (!match || (!match[2] && !match[3])) {
+		throw new Error(`Unparseable amount: ${JSON.stringify(amount)}`);
+	}
+	const [, sign, whole = '', fracRaw = ''] = match;
 	const frac = (fracRaw + '00').slice(0, 2);
-	let cents = Number(whole) * 100 + Number(frac);
+	let cents = Number(whole || '0') * 100 + Number(frac);
 	if (fracRaw.length > 2 && Number(fracRaw[2]) >= 5) cents += 1;
 	return sign === '-' ? -cents : cents;
 }
diff --git a/src/lib/server/services/sync.ts b/src/lib/server/services/sync.ts
index a9246b5..36fd06b 100644
--- a/src/lib/server/services/sync.ts
+++ b/src/lib/server/services/sync.ts
@@ -5,8 +5,11 @@ import { listConnections } from './connections.ts';
 import { appendCategorizationEvent } from './categorization.ts';
 import { applyRulesToUncategorized } from './rules.ts';
 
-const FIRST_SYNC_LOOKBACK_DAYS = 365;
-const INCREMENTAL_OVERLAP_DAYS = 30;
+// Always request a full year. Household-scale payloads are small, upserts are
+// idempotent, and a fixed window means a bank added to the connection later
+// still gets its full backfill (a shorter incremental window would truncate
+// new accounts' history to the overlap).
+const SYNC_LOOKBACK_DAYS = 365;
 /** Max gap between a pending transaction and the posted one replacing it. */
 const RECONCILE_WINDOW_DAYS = 5;
 
@@ -39,11 +42,7 @@ async function syncConnection(
 	accessUrl: string,
 	fetchFn: typeof fetch
 ): Promise<SyncOutcome> {
-	const hasPriorSync = db
-		.prepare('SELECT 1 FROM raw_syncs WHERE connection_id = ? AND ok = 1 LIMIT 1')
-		.get(connectionId);
-	const lookbackDays = hasPriorSync ? INCREMENTAL_OVERLAP_DAYS : FIRST_SYNC_LOOKBACK_DAYS;
-	const startDate = new Date(Date.now() - lookbackDays * 86400_000);
+	const startDate = new Date(Date.now() - SYNC_LOOKBACK_DAYS * 86400_000);
 
 	const fetched = await fetchAccounts(accessUrl, { startDate, pending: true }, fetchFn);
 	const fetchedAt = new Date().toISOString();