diff --git a/scripts/dashboards_render_atlas.py b/scripts/dashboards_render_atlas.py
index c55ba96c..bd40f6e4 100644
--- a/scripts/dashboards_render_atlas.py
+++ b/scripts/dashboards_render_atlas.py
@@ -1442,7 +1442,7 @@ def build_overview():
             "decimals": 4,
             "text_mode": "value",
             "instant": True,
-            "description": "Rolling 365-day availability from vmalert's precomputed atlas:availability:ratio_365d series. Missing pre-telemetry slots are filled as 100% up, and Grafana reads the latest recorded value instead of recomputing a year of raw samples.",
+            "description": "Rolling 365-day availability from vmalert's precomputed atlas:availability:ratio_365d series. Missing slots before the first raw availability sample are filled as 100% up; missing slots after that first sample count as down.",
         },
         {
             "id": 4,
diff --git a/scripts/tests/test_dashboards_render_atlas.py b/scripts/tests/test_dashboards_render_atlas.py
index 162827aa..9a9903a3 100644
--- a/scripts/tests/test_dashboards_render_atlas.py
+++ b/scripts/tests/test_dashboards_render_atlas.py
@@ -59,7 +59,7 @@ def test_overview_availability_panel_uses_recorded_365d_rollup():
     assert panel["targets"][0]["expr"] == 'last_over_time(atlas:availability:ratio_365d{scope="atlas"}[30m])'
     assert panel["targets"][0]["instant"] is True
     assert "precomputed" in panel["description"]
-    assert "pre-telemetry" in panel["description"]
+    assert "after that first sample count as down" in panel["description"]
 
 
 def test_render_configmap_writes(tmp_path):
diff --git a/services/monitoring/dashboards/atlas-overview.json b/services/monitoring/dashboards/atlas-overview.json
index 373f456e..641dad19 100644
--- a/services/monitoring/dashboards/atlas-overview.json
+++ b/services/monitoring/dashboards/atlas-overview.json
@@ -283,7 +283,7 @@
         },
         "textMode": "value"
       },
-      "description": "Rolling 365-day availability from vmalert's precomputed atlas:availability:ratio_365d series. Missing pre-telemetry slots are filled as 100% up, and Grafana reads the latest recorded value instead of recomputing a year of raw samples."
+      "description": "Rolling 365-day availability from vmalert's precomputed atlas:availability:ratio_365d series. Missing slots before the first raw availability sample are filled as 100% up; missing slots after that first sample count as down."
     },
     {
       "id": 4,
diff --git a/services/monitoring/grafana-dashboard-overview.yaml b/services/monitoring/grafana-dashboard-overview.yaml
index 64d3bd88..4a5b9606 100644
--- a/services/monitoring/grafana-dashboard-overview.yaml
+++ b/services/monitoring/grafana-dashboard-overview.yaml
@@ -292,7 +292,7 @@ data:
             },
             "textMode": "value"
           },
-          "description": "Rolling 365-day availability from vmalert's precomputed atlas:availability:ratio_365d series. Missing pre-telemetry slots are filled as 100% up, and Grafana reads the latest recorded value instead of recomputing a year of raw samples."
+          "description": "Rolling 365-day availability from vmalert's precomputed atlas:availability:ratio_365d series. Missing slots before the first raw availability sample are filled as 100% up; missing slots after that first sample count as down."
         },
         {
           "id": 4,
diff --git a/services/monitoring/vmalert-atlas-availability.yaml b/services/monitoring/vmalert-atlas-availability.yaml
index 272fe314..549ffcb1 100644
--- a/services/monitoring/vmalert-atlas-availability.yaml
+++ b/services/monitoring/vmalert-atlas-availability.yaml
@@ -30,23 +30,58 @@ data:
               rollup: hourly
           - record: atlas:availability:ratio_365d
             expr: |
-              (
+              clamp_max((
                 (
-                  sum(sum_over_time(atlas:availability:ratio_1h{scope="atlas",rollup="hourly"}[365d]))
+                  sum(sum_over_time((
+                    min(
+                      (
+                        sum(kube_node_status_condition{condition="Ready",status="true",node=~"titan-0a|titan-0b|titan-0c"})
+                        / 3
+                      ),
+                      (
+                        sum(kube_deployment_status_replicas_available{namespace=~"traefik|kube-system",deployment="traefik"})
+                        / clamp_min(sum(kube_deployment_spec_replicas{namespace=~"traefik|kube-system",deployment="traefik"}), 1)
+                      )
+                    )
+                  )[365d:1h]))
                   or on() vector(0)
                 )
                 +
                 clamp_min(
-                  35040
+                  8761
                   -
                   (
-                    sum(count_over_time(atlas:availability:ratio_1h{scope="atlas",rollup="hourly"}[365d]))
-                    or on() vector(0)
+                    clamp_min(
+                      floor(
+                        (
+                          time()
+                          -
+                          (
+                            min(min_over_time(timestamp(
+                              min(
+                                (
+                                  sum(kube_node_status_condition{condition="Ready",status="true",node=~"titan-0a|titan-0b|titan-0c"})
+                                  / 3
+                                ),
+                                (
+                                  sum(kube_deployment_status_replicas_available{namespace=~"traefik|kube-system",deployment="traefik"})
+                                  / clamp_min(sum(kube_deployment_spec_replicas{namespace=~"traefik|kube-system",deployment="traefik"}), 1)
+                                )
+                              )
+                            )[365d:1h]))
+                            or on() vector(time() + 3600)
+                          )
+                        )
+                        / 3600
+                      )
+                      + 1,
+                      0
+                    )
                   ),
                   0
                 )
               )
-              / 35040
+              / 8761, 1)
             labels:
               scope: atlas
               rollup: yearly
@@ -79,7 +114,7 @@ spec:
       labels:
         app: vmalert-atlas-availability
       annotations:
-        bstein.dev/rules-revision: "2026-05-10-availability-rollup-v4"
+        bstein.dev/rules-revision: "2026-05-10-availability-rollup-v5"
     spec:
       serviceAccountName: vmalert-atlas-availability
       affinity: