diff --git a/docs/release-control/v6/internal/subsystems/monitoring.md b/docs/release-control/v6/internal/subsystems/monitoring.md
index b6d5ff16cd..28d198cc51 100644
--- a/docs/release-control/v6/internal/subsystems/monitoring.md
+++ b/docs/release-control/v6/internal/subsystems/monitoring.md
@@ -323,7 +323,9 @@ Verification: `internal/truenas/core_reporting_test.go` and its anonymised
 `testdata/core13_reporting.json` cover five source-bound native excerpts,
 row/timing/alias/zero/null/empty/finite controls, device totals, stale buckets,
 ARC alignment, current and canonical History projections, request validation,
-catalogue limits and failure boundaries. The excerpt windows are deliberately
+catalogue limits and failure boundaries. Unique overflow is rejected rather than
+truncated, while duplicate identifiers consume only one selection entry. The
+excerpt windows are deliberately
 shortened controls, not complete native windows. Extended
 `TestTrueNASPartialReportingPipeline` in
 `internal/monitoring/truenas_poller_test.go` crosses pinned-certificate HTTP,
diff --git a/internal/truenas/client.go b/internal/truenas/client.go
index 769c78e744..3c932617b1 100644
--- a/internal/truenas/client.go
+++ b/internal/truenas/client.go
@@ -426,7 +426,8 @@ func legacyRESTReportingGraphs() []map[string]any {
 // getLegacySystemReportingData keeps a rejected optional graph from discarding
 // usable CPU/memory readings. Keep the successful batch fast path; only split
 // graph-validation/server errors, never authentication, rate-limit, endpoint,
-// transport or cancellation failures. The query and graph set remain unchanged.
+// transport or cancellation failures. Bind the catalogue-selected graph set once
+// for both the batch and split; the requested query window remains unchanged.
 func (c *Client) getLegacySystemReportingData(ctx context.Context, query map[string]any) ([]trueNASReportingGetDataResponse, error) {
 	graphs, err := c.legacyReportingGraphs(ctx)
 	if err != nil {
diff --git a/internal/truenas/core_reporting_test.go b/internal/truenas/core_reporting_test.go
index 07ee611c7e..f9cc2f5864 100644
--- a/internal/truenas/core_reporting_test.go
+++ b/internal/truenas/core_reporting_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"math"
 	"net/http"
 	"os"
@@ -378,6 +379,22 @@ func TestCORE13CatalogueAndResponseSafety(t *testing.T) {
 	client.Close()
 }
 
+func TestCORE13CatalogueRejectsUniqueOverflow(t *testing.T) {
+	identifiers := make([]string, 253)
+	for i := range identifiers {
+		identifiers[i] = fmt.Sprintf("disk-%d", i)
+	}
+	raw, err := json.Marshal([]map[string]any{{"name": "disk", "identifiers": identifiers}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	client := newLegacyRESTReportingClient(t, alertArgsTransport{"/api/v2.0/reporting/graphs": {body: string(raw)}})
+	defer client.Close()
+	if graphs, err := client.legacyReportingGraphs(context.Background()); err == nil || graphs != nil {
+		t.Fatal("oversized unique catalogue became a partial host total")
+	}
+}
+
 func TestCORE13ARCAlignedWithFreeMemory(t *testing.T) {
 	replies := core13ReportingFixture(t)
 	history := parseSystemMetricHistory(replies)