diff --git a/src/dls_tiled/visr.py b/src/dls_tiled/visr.py
index 0976cb0..e84f11e 100644
--- a/src/dls_tiled/visr.py
+++ b/src/dls_tiled/visr.py
@@ -104,6 +104,27 @@ async def _shared(key: tuple, compute):
     return await asyncio.shield(task)
 
 
+async def _run_progress(root, uid) -> tuple:
+    """How far a run has got, as its catalog records it: whether it has a stop
+    document, and the shape of its camera's ``RedTotal`` (one entry per point).
+
+    Part of the key of a shared result, so a result is never reused once the run
+    has moved on. Without it, the poll a UI makes when a scan ends could be
+    given the result of the poll just before, computed without the last points.
+    Anything that can't be looked up counts as unknown (``None``)."""
+    try:
+        run = await root.lookup_adapter([uid])
+        stopped = bool((run.metadata() or {}).get("stop"))
+    except Exception:
+        return (None, None)
+    try:
+        camera = await root.lookup_adapter([uid, "primary", "RedTotal"])
+        shape = tuple(camera.structure().shape)
+    except Exception:
+        shape = None
+    return (stopped, shape)
+
+
 async def _compute_and_keep(key: tuple, compute):
     try:
         result = await compute()
@@ -653,12 +674,17 @@ async def binned(  # type: ignore
 
     # A UI polls this several times a second per client while points arrive only
     # every couple of seconds, so identical requests share one computation (and
-    # one read of the files) and its result is reused for a moment.
+    # one read of the files) and its result is reused for a moment, but only
+    # while the run is where it was (see _run_progress).
     # The key leaves out who is asking. That is safe only because the data is
     # read through root_tree.lookup_adapter, which bypasses Tiled's access policy
     # anyway; if per-run access control is added, the key needs the principal
     # (or its access tags), or one user's result could be served to another.
-    key = (uid, tuple(sorted(request.query_params.multi_items())))
+    key = (
+        uid,
+        tuple(sorted(request.query_params.multi_items())),
+        await _run_progress(root, uid),
+    )
 
     async def compute():
         output = await _binned_output(
@@ -1167,7 +1193,12 @@ async def render(  # type: ignore
     root = request.app.state.root_tree
     uid = [s for s in path.strip("/").split("/") if s][0]
     # Shared like /binned's results, and with the same caveat about access control.
-    key = ("render", uid, tuple(sorted(request.query_params.multi_items())))
+    key = (
+        "render",
+        uid,
+        tuple(sorted(request.query_params.multi_items())),
+        await _run_progress(root, uid),
+    )
 
     async def compute():
         points = await load_points(
diff --git a/tests/test_visr.py b/tests/test_visr.py
index f26ef45..bb99041 100644
--- a/tests/test_visr.py
+++ b/tests/test_visr.py
@@ -636,6 +636,63 @@ async def scenario():
     assert compute.calls == 2
 
 
+def grow_grid_scan(client, uid, n_from, n_to):
+    """Append points n_from..n_to of write_grid_scan's raster to a run, as a
+    scan in progress does"""
+    primary = client[uid]["primary"]
+    x = numpy.array([0.0, 1.0, 2.0] * 3)[n_from:n_to]
+    y = numpy.repeat([0.0, 1.0, 2.0], 3)[n_from:n_to]
+    primary["X"].patch(x, offset=n_from, extend=True)
+    primary["Y"].patch(y, offset=n_from, extend=True)
+    for channel in ("RedTotal", "GreenTotal", "BlueTotal"):
+        primary[channel].patch(
+            numpy.arange(9.0)[n_from:n_to], offset=n_from, extend=True
+        )
+
+
+@pytest.mark.parametrize("route", ["binned", "render"])
+def test_a_shared_result_is_not_reused_once_the_run_has_grown(
+    client, monkeypatch, route
+):
+    monkeypatch.setattr(visr, "BINNED_CACHE_SECONDS", 60.0)
+    write_grid_scan(client, "growing", 7)
+    http = client.context.http_client
+
+    before = http.get(f"/api/v1/{route}/growing").json()
+    grow_grid_scan(client, "growing", 7, 9)
+    after = http.get(f"/api/v1/{route}/growing").json()
+
+    assert (before["n_points"], after["n_points"]) == (7, 9)
+
+
+def test_a_shared_result_is_not_reused_once_the_run_has_stopped(client, monkeypatch):
+    monkeypatch.setattr(visr, "BINNED_CACHE_SECONDS", 60.0)
+    write_grid_scan(client, "ending", 9)
+    http = client.context.http_client
+    compute = []
+    real = visr._binned_output
+
+    async def counting(*args):
+        compute.append(1)
+        return await real(*args)
+
+    monkeypatch.setattr(visr, "_binned_output", counting)
+
+    http.get("/api/v1/binned/ending")
+    http.get("/api/v1/binned/ending")  # reused
+    run = client["ending"]
+    run.update_metadata(metadata={**run.metadata, "stop": {"exit_status": "success"}})
+    http.get("/api/v1/binned/ending")
+
+    assert len(compute) == 2
+
+
+def test_run_progress_is_unknown_for_a_run_that_is_not_there(client):
+    root = client.context.http_client.app.state.root_tree
+
+    assert asyncio.run(visr._run_progress(root, "nowhere")) == (None, None)
+
+
 def test_binned_has_an_etag_and_answers_304_when_nothing_changed(client, monkeypatch):
     monkeypatch.setattr(visr, "BINNED_CACHE_SECONDS", 0.5)
     write_grid_scan(client, "grid", 9)