diff --git a/src/lib/measurements/__tests__/daily-series-read-tiered.test.ts b/src/lib/measurements/__tests__/daily-series-read-tiered.test.ts
index dca7b0525..7a494c151 100644
--- a/src/lib/measurements/__tests__/daily-series-read-tiered.test.ts
+++ b/src/lib/measurements/__tests__/daily-series-read-tiered.test.ts
@@ -112,7 +112,10 @@ describe("readDailySeries — long-range tier step-up", () => {
     });
 
     expect(mocks.readTieredRollupSeries).toHaveBeenCalledTimes(1);
-    expect(mocks.readTieredRollupSeries.mock.calls[0][0].windowDays).toBe(3650);
+    // v1.26.0 SEAM-N2 — the resolved `[from, to]` bounds are threaded so the
+    // tier reads the REQUESTED window, not a trailing "to now" slice.
+    expect(mocks.readTieredRollupSeries.mock.calls[0][0].from).toBe(from);
+    expect(mocks.readTieredRollupSeries.mock.calls[0][0].to).toBe(to);
     // Whole-history coverage: the earliest 2017 bucket survives.
     expect(result[0].measuredAt).toBe("2017-01-01T00:00:00.000Z");
     expect(result).toHaveLength(2);
diff --git a/src/lib/measurements/daily-series-read.ts b/src/lib/measurements/daily-series-read.ts
index 8759c4e72..98cafad59 100644
--- a/src/lib/measurements/daily-series-read.ts
+++ b/src/lib/measurements/daily-series-read.ts
@@ -79,7 +79,12 @@ export async function readDailySeries(opts: {
     const tiered = await readTieredRollupSeries({
       userId,
       type,
-      windowDays: windowDaysFull,
+      // v1.26.0 SEAM-N2 — pass the resolved `[from, to]` bounds so the tier
+      // reads the REQUESTED window (which may be entirely historic), not a
+      // trailing "to now" slice. `windowDaysFull` still gates entry above and
+      // drives the tier width inside the reader.
+      from,
+      to,
       priorityJson,
     });
     if (tiered && tiered.rows.length > 0) {
diff --git a/src/lib/rollups/__tests__/measurement-read-wmy.test.ts b/src/lib/rollups/__tests__/measurement-read-wmy.test.ts
index 733937bb6..67826add9 100644
--- a/src/lib/rollups/__tests__/measurement-read-wmy.test.ts
+++ b/src/lib/rollups/__tests__/measurement-read-wmy.test.ts
@@ -296,12 +296,23 @@ describe("readBestGranularityRollups — cross-consumer routing parity", () => {
  * miss; and that the wire shape mirrors the daily reader.
  */
 describe("readTieredRollupSeries", () => {
+  const DAY_MS = 86_400_000;
+  // A fixed "now-ish" anchor for the current-window cases; the historic case
+  // uses its own explicit past bounds. Nothing in the reader reads
+  // `Date.now()` any more, so these are just span endpoints.
+  const NOW = new Date("2026-06-21T00:00:00.000Z");
+  const win = (days: number, to: Date = NOW) => ({
+    from: new Date(to.getTime() - days * DAY_MS),
+    to,
+  });
+
   it("returns null on a non-positive window without touching the db", async () => {
     expect(
       await readTieredRollupSeries({
         userId: "u",
         type: "WEIGHT",
-        windowDays: 0,
+        from: NOW,
+        to: NOW,
       }),
     ).toBeNull();
     expect(findMany).not.toHaveBeenCalled();
@@ -320,7 +331,7 @@ describe("readTieredRollupSeries", () => {
     const result = await readTieredRollupSeries({
       userId: "u",
       type: "WEIGHT",
-      windowDays: 3650,
+      ...win(3650),
     });
 
     expect(result).not.toBeNull();
@@ -332,12 +343,59 @@ describe("readTieredRollupSeries", () => {
     expect(result?.rows.length).toBe(10);
   });
 
+  // v1.26.0 SEAM-N2 — a historic window entirely in the past must bound the
+  // rollup read on BOTH ends. Pre-fix the reader anchored on `now − windowDays`
+  // and would have queried `bucketStart >= now − 730d` (mid-2024 onward),
+  // returning recent buckets for a 2020–2022 ask.
+  it("bounds the rollup read on BOTH ends for a historic past window", async () => {
+    const from = new Date("2020-01-01T00:00:00.000Z");
+    const to = new Date("2022-01-01T00:00:00.000Z");
+    const inWindow: RollupBucketRow[] = [
+      bucket("2020-02-01T00:00:00.000Z", { count: 12, mean: 80 }),
+      bucket("2021-06-01T00:00:00.000Z", { count: 12, mean: 81 }),
+      bucket("2021-12-01T00:00:00.000Z", { count: 12, mean: 82 }),
+    ];
+    findMany.mockResolvedValueOnce(inWindow);
+
+    const result = await readTieredRollupSeries({
+      userId: "u",
+      type: "WEIGHT",
+      from,
+      to,
+    });
+
+    // The `bucketStart` filter carries BOTH the requested lower AND upper
+    // bound — not a trailing "to now" slice.
+    const where = findMany.mock.calls[0][0].where;
+    expect(where.bucketStart).toEqual({ gte: from, lte: to });
+    // Every returned bucket_start falls inside the requested window.
+    for (const row of result?.rows ?? []) {
+      const t = new Date(row.measuredAt).getTime();
+      expect(t).toBeGreaterThanOrEqual(from.getTime());
+      expect(t).toBeLessThanOrEqual(to.getTime());
+    }
+    // Tier width is 2 years (731 days) → still the MONTH tier for >730 d.
+    expect(result?.granularity).toBe("MONTH");
+  });
+
+  // The web-chart "All" path passes `to ≈ now`; prove that case still bounds
+  // on both ends (no regression) — the historic fix must not perturb it.
+  it("bounds a current-window (to = now) read on both ends too", async () => {
+    findMany.mockResolvedValueOnce([bucket("2026-01-01T00:00:00.000Z")]);
+    const { from, to } = win(3650);
+    await readTieredRollupSeries({ userId: "u", type: "WEIGHT", from, to });
+    expect(findMany.mock.calls[0][0].where.bucketStart).toEqual({
+      gte: from,
+      lte: to,
+    });
+  });
+
   it("reads the WEEK tier for a 1–2 year window", async () => {
     findMany.mockResolvedValueOnce([bucket("2025-08-04T00:00:00.000Z")]);
     const result = await readTieredRollupSeries({
       userId: "u",
       type: "WEIGHT",
-      windowDays: 540,
+      ...win(540),
     });
     expect(result?.granularity).toBe("WEEK");
     expect(findMany.mock.calls[0][0].where.granularity).toBe("WEEK");
@@ -351,7 +409,7 @@ describe("readTieredRollupSeries", () => {
     const result = await readTieredRollupSeries({
       userId: "u",
       type: "WEIGHT",
-      windowDays: 3650,
+      ...win(3650),
     });
     expect(result?.granularity).toBe("DAY");
     expect(findMany.mock.calls[0][0].where.granularity).toBe("MONTH");
@@ -364,7 +422,7 @@ describe("readTieredRollupSeries", () => {
     const result = await readTieredRollupSeries({
       userId: "u",
       type: "WEIGHT",
-      windowDays: 3650,
+      ...win(3650),
     });
     expect(result).toBeNull();
     // MONTH, WEEK, DAY all probed (never coarser than the target).
@@ -384,7 +442,7 @@ describe("readTieredRollupSeries", () => {
     const result = await readTieredRollupSeries({
       userId: "u",
       type: "ACTIVITY_STEPS",
-      windowDays: 3650,
+      ...win(3650),
     });
     expect(result?.rows[0].value).toBe(240_000);
     expect(result?.rows[0].minValue).toBeUndefined();
@@ -403,7 +461,7 @@ describe("readTieredRollupSeries", () => {
     const result = await readTieredRollupSeries({
       userId: "u",
       type: "WEIGHT",
-      windowDays: 3650,
+      ...win(3650),
     });
     expect(result?.rows[0].value).toBe(81.5);
     expect(result?.rows[0].minValue).toBe(78);
diff --git a/src/lib/rollups/measurement-read-wmy.ts b/src/lib/rollups/measurement-read-wmy.ts
index 46eb1235d..779adf443 100644
--- a/src/lib/rollups/measurement-read-wmy.ts
+++ b/src/lib/rollups/measurement-read-wmy.ts
@@ -164,6 +164,10 @@ export async function readBestGranularityRollups(
       type,
       floor.granularity,
       since,
+      // Trailing-window semantics: no upper bound. This router serves the
+      // "last N days to now" probes (summaries-slice / health-score); the
+      // requested-window bounding lives on `readTieredRollupSeries`.
+      null,
       priority,
     );
     if (rows && rows.length > 0) {
@@ -229,20 +233,27 @@ async function readGranularity(
   userId: string,
   type: MeasurementType,
   granularity: RollupGranularity,
-  since: Date,
+  from: Date,
+  to: Date | null,
   userPriorityJson: unknown,
 ): Promise<RollupBucketRow[] | null> {
   // Bounded `findMany`: `(userId, type, granularity, bucketStart, source)`
   // is the composite primary key so the planner picks the index path
-  // every time. `bucketStart >= since` is the same shape
-  // `readRollupBuckets` uses; we don't carry an upper bound because
-  // the helpers are always reading "trailing window to now".
+  // every time. When `to` is supplied the `bucketStart` filter is bounded
+  // on BOTH ends (`gte from` AND `lte to`) so a caller asking for an
+  // arbitrary historic window — `[2020-01-01, 2022-01-01]` — reads the
+  // buckets INSIDE that window rather than the trailing "to now" slice.
+  // This mirrors the DAY-tier `readRollup` in `daily-series-read.ts`
+  // (`bucketStart: { gte: from, lte: to }`) so the tiered read reproduces
+  // the same window contract the live-SQL fallback bounds on both ends.
+  // `to === null` keeps the legacy trailing-window semantics for the
+  // `readBestGranularityRollups` router.
   const rows = await prisma.measurementRollup.findMany({
     where: {
       userId,
       type,
       granularity,
-      bucketStart: { gte: since },
+      bucketStart: to === null ? { gte: from } : { gte: from, lte: to },
     },
     orderBy: { bucketStart: "asc" },
     select: {
@@ -346,20 +357,32 @@ const TIER_ORDER: RollupGranularity[] = ["DAY", "WEEK", "MONTH", "YEAR"];
  * (≤ ~104 weeks for the WEEK tier, ≤ ~12 months/year for MONTH). If a
  * future tier ever risks an unbounded count it must step coarser rather
  * than truncate; no silent cap lives on this path.
+ *
+ * v1.26.0 SEAM-N2 — the reader is bounded to the REQUESTED `[from, to]`
+ * window on BOTH ends, not a trailing "now − windowDays … now" slice.
+ * The caller passes arbitrary ISO instants (a historic "All" range whose
+ * `to` need not be ≈ now), so anchoring on `Date.now()` returned the wrong
+ * buckets entirely. The tier SELECTION still keys off the window WIDTH
+ * (`windowDays`, derived from the span) — only the window the tier READS
+ * changed. This matches the DAY-tier `readRollup` + the live-SQL
+ * `readLiveDaily` fallback, both of which bound on `[from, to]`.
  */
 export async function readTieredRollupSeries(opts: {
   userId: string;
   type: MeasurementType;
-  windowDays: number;
+  from: Date;
+  to: Date;
   priorityJson?: unknown;
 }): Promise<{
   granularity: RollupGranularity;
   rows: TieredSeriesRow[];
 } | null> {
-  const { userId, type, windowDays, priorityJson } = opts;
+  const { userId, type, from, to, priorityJson } = opts;
+  // Tier selection keys off the window WIDTH; derive it the same way the
+  // caller (`daily-series-read`) does so the chosen tier is identical.
+  const windowDays = Math.ceil((to.getTime() - from.getTime()) / 86_400_000);
   if (!Number.isFinite(windowDays) || windowDays <= 0) return null;
 
-  const since = new Date(Date.now() - windowDays * 24 * 60 * 60 * 1000);
   const priority =
     priorityJson !== undefined
       ? priorityJson
@@ -375,7 +398,8 @@ export async function readTieredRollupSeries(opts: {
       userId,
       type,
       granularity,
-      since,
+      from,
+      to,
       priority,
     );
     if (rows && rows.length > 0) {