diff --git a/docs/release-control/v6/internal/subsystems/monitoring.md b/docs/release-control/v6/internal/subsystems/monitoring.md
index 50ea99e48..11f407d7a 100644
--- a/docs/release-control/v6/internal/subsystems/monitoring.md
+++ b/docs/release-control/v6/internal/subsystems/monitoring.md
@@ -496,7 +496,13 @@ changes.
    fixture registries synced in `internal/mock/metric_personas.go`, never a
    per-call fixture graph clone on the chart path. A percentage series without
    its byte companion silently empties the host-capacity memory column instead
-   of degrading it.
+   of degrading it. The same obligation is general. Seeded coverage in
+   `internal/monitoring/mock_metrics_history.go` and the synthetic generator
+   must carry the same series set per resource kind, so a chart window never
+   decides whether a series exists. Docker hosts seed disk and network I/O for
+   that reason, matching what the agent reports on a real host. A series
+   present on one range and absent on another reads as a broken column, not as
+   missing history.
    Discovery config and configured-host IP resolution must stay off the
    monitor lock. `internal/monitoring/monitor_discovery_helpers.go` exposes
    the canonical `discoveryConfigSnapshot()` that discovery providers consume,
diff --git a/internal/monitoring/mock_metrics_history.go b/internal/monitoring/mock_metrics_history.go
index dadbaa087..0d45f7ff7 100644
--- a/internal/monitoring/mock_metrics_history.go
+++ b/internal/monitoring/mock_metrics_history.go
@@ -914,13 +914,16 @@ func seedMockMetricsHistory(mh *MetricsHistory, ms *metrics.Store, graph mock.Fi
 			continue
 		}
 
+		// Docker hosts report disk and network I/O through the agent, and the
+		// synthetic generator emits both beyond the seeded window. Seeding the
+		// same series keeps short ranges from being the only ones missing them.
 		recordGuest(
 			[]string{"dockerHost:" + host.ID},
 			"dockerHost",
 			host.ID,
 			true,
-			false,
-			false,
+			true,
+			true,
 		)
 
 		for _, container := range host.Containers {
diff --git a/internal/monitoring/mock_metrics_history_test.go b/internal/monitoring/mock_metrics_history_test.go
index 22246f52b..1484fa78b 100644
--- a/internal/monitoring/mock_metrics_history_test.go
+++ b/internal/monitoring/mock_metrics_history_test.go
@@ -1989,3 +1989,29 @@ func TestSeedMockMetricsHistory_DiskTelemetryParityAcrossNativeAndTrueNAS(t *tes
 		}
 	}
 }
+
+// Seeded mock history and the synthetic generator must agree on which series a
+// resource carries. Docker hosts previously seeded cpu, memory, and disk only,
+// so their I/O series existed on ranges past the seed window and nowhere else.
+func TestMockDockerHostSeedCoversTheSameSeriesAsTheSyntheticGenerator(t *testing.T) {
+	previous := mock.IsMockEnabled()
+	mustSetMockEnabled(t, true)
+	defer mustSetMockEnabled(t, previous)
+
+	history := NewMetricsHistory(4096, 24*time.Hour)
+	graph := mock.CurrentFixtureGraph()
+	if len(graph.State.DockerHosts) == 0 {
+		t.Fatal("mock fixture graph has no docker hosts")
+	}
+
+	now := time.Now().UTC()
+	seedMockMetricsHistory(history, nil, graph, now, 2*time.Hour, time.Minute)
+
+	hostID := graph.State.DockerHosts[0].ID
+	for _, metricType := range mockGuestChartMetricTypes {
+		points := history.GetGuestMetrics("dockerHost:"+hostID, metricType, 2*time.Hour)
+		if len(points) == 0 {
+			t.Fatalf("seeded docker host %s is missing the %s series", hostID, metricType)
+		}
+	}
+}