diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29e109d..34a4612 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ so entries say what changed, cite the issue, and stop.
 - `labels-reconcile` — a degraded mergeability/checks read now logs gh's actual stderr (collapsed, bounded) beside the byte-identical counted line, and the blind-sweep warning leads with the observed reason instead of asserting the permissions cause (#101).
 - `LABELS.md` — drop the vendored scope-table enumeration; the per-repo set lives in `.github/labels.conf` and the repo's own CONTRIBUTING (#104).
 - Changelog publication — count entries instead of bytes, refuse dangling grouped headings, and seed grouped re-arms with Added/Changed/Fixed (#98).
+- `labels-reconcile` — warn once per sweep when a repository lacks labels declared by the pinned core taxonomy (#105).
 - `labels-reconcile` — grant callers private-repo check reads and warn when an entire PR sweep is blind (#95).
 - `labels-reconcile` — the bootstrap now retires the six GitHub defaults `LABELS.md` publishes as deleted, tolerating both an already-absent label and a refused delete (#93).
 - `issueflow-reconcile` — a triage-authored issue arrival stands down with exit 0 instead of killing the run before the sweep (#91).
diff --git a/LABELS.md b/LABELS.md
index 70f586d..fc5830b 100644
--- a/LABELS.md
+++ b/LABELS.md
@@ -188,7 +188,8 @@ on a PR would say the same thing twice and drift.
 
 The labels workflow (issue #10) recomputes PR state statelessly on PR events
 plus a 15-minute advisory cron, and bootstraps this taxonomy idempotently on
-manual dispatch. The same workflow reconciles issue-flow labels on issue
-events and during the scheduled sweep. Default GitHub labels (`duplicate`, `invalid`,
-`question`, `wontfix`, `help wanted`, `good first issue`) are deleted at
-bootstrap — a `question` is a discussion, not an issue.
+manual dispatch. The sweep warns when the core taxonomy declares a label the
+repository lacks. The same workflow reconciles issue-flow labels on issue
+events and during the scheduled sweep. Default GitHub labels (`duplicate`,
+`invalid`, `question`, `wontfix`, `help wanted`, `good first issue`) are
+deleted at bootstrap — a `question` is a discussion, not an issue.
diff --git a/actions/labels-reconcile/labels-reconcile.sh b/actions/labels-reconcile/labels-reconcile.sh
index 87c301e..d02e6aa 100755
--- a/actions/labels-reconcile/labels-reconcile.sh
+++ b/actions/labels-reconcile/labels-reconcile.sh
@@ -96,6 +96,21 @@ read_failure_reason() { # $1 = captured stderr → one bounded line; pure (#101)
   fi
 }
 
+missing_core_labels_warning() { # $1 = declared rows, $2 = repo label names
+  local rows="$1" repo_labels="$2" row name missing=""
+  [ -n "$repo_labels" ] || return 0
+  while IFS= read -r row; do
+    [ -n "$row" ] || continue
+    name="${row%%|*}"
+    if ! grep -qxF "$name" <<<"$repo_labels"; then
+      if [ -n "$missing" ]; then missing="$missing, $name"; else missing="$name"; fi
+    fi
+  done <<<"$rows"
+  if [ -n "$missing" ]; then
+    echo "::warning::labels: missing core label(s): $missing; bump the ceremony pin, then re-dispatch workflow_dispatch to bootstrap the taxonomy"
+  fi
+}
+
 load_config() { # $1 = consumer labels.conf; panel is mandatory, scopes optional
   local conf="$1" line panel_seen=false
   [ -f "$conf" ] || {
@@ -627,6 +642,7 @@ main() {
   # add against it, because one unknown name fails the whole edit call.
   REPO_LABELS="$(gh label list -R "$REPO" --limit 200 --json name --jq '.[].name' 2>/dev/null || echo "")"
   [ -z "$REPO_LABELS" ] && log "WARNING: could not read the label set — applying labels unfiltered"
+  missing_core_labels_warning "$(core_label_rows)" "$REPO_LABELS"
 
   local n output status total=0 unreadable=0 sampled_reason=""
   while IFS= read -r n; do
diff --git a/docs/CONSUMERS.md b/docs/CONSUMERS.md
index efad3f8..2b285bc 100644
--- a/docs/CONSUMERS.md
+++ b/docs/CONSUMERS.md
@@ -319,7 +319,10 @@ rows remain consumer-owned because paths and surfaces differ by repository.
 
 After adding the caller and configuration, run `workflow_dispatch` once to
 bootstrap labels on a fresh repository. Scheduled and PR-triggered runs only
-reconcile; they do not repeatedly upsert the taxonomy.
+reconcile; they do not repeatedly upsert the taxonomy. When a ceremony pin
+bump adds a core label, bump the pin first and then re-dispatch
+`workflow_dispatch`; the scheduled sweep warns when the pinned taxonomy
+declares a core label the repository lacks.
 
 ## Doctrine mirror
 
diff --git a/test/labels-reconcile.test.sh b/test/labels-reconcile.test.sh
index 8b1849f..4cb1c14 100755
--- a/test/labels-reconcile.test.sh
+++ b/test/labels-reconcile.test.sh
@@ -74,6 +74,24 @@ expect "...within the 304-byte bound" yes \
 exact_reason="$(read_failure_reason "$(printf 'e%.0s' {1..300})")"
 expect "a 300-char reason passes through whole" 300 "${#exact_reason}"
 
+# -- a missing core taxonomy row is visible without mutating labels ----------
+core_rows="$(core_label_rows)"
+core_names="$(cut -d'|' -f1 <<<"$core_rows")"
+expect "a complete core taxonomy does not warn" "" \
+  "$(missing_core_labels_warning "$core_rows" "$core_names")"
+expect "one missing core label is named exactly" \
+  "::warning::labels: missing core label(s): attention; bump the ceremony pin, then re-dispatch workflow_dispatch to bootstrap the taxonomy" \
+  "$(missing_core_labels_warning "$core_rows" "$(grep -vxF attention <<<"$core_names")")"
+expect "three missing core labels are named in table order" \
+  "::warning::labels: missing core label(s): offsite, needs-ruling, attention; bump the ceremony pin, then re-dispatch workflow_dispatch to bootstrap the taxonomy" \
+  "$(missing_core_labels_warning "$core_rows" "$(grep -vxF -e offsite -e needs-ruling -e attention <<<"$core_names")")"
+expect "an unreadable empty label set does not report the taxonomy missing" "" \
+  "$(missing_core_labels_warning "$core_rows" "")"
+expect "unrelated scope labels do not affect a complete core taxonomy" "" \
+  "$(missing_core_labels_warning "$core_rows" "$core_names
+scope:consumer-one
+scope:consumer-two")"
+
 # -- drafts are building, whoever is requested --------------------------------
 DRAFT=true HEAD_SHA=head1 REQUESTED="" REVIEWS_JSON='[]'
 expect "draft PR is building" state:building "$(decide_state)"
@@ -636,7 +654,7 @@ blind_main_probe() {
     LABELS_CONF=.github/labels.conf
     gh() {
       if [ "$1" = label ] && [ "$2" = list ]; then
-        printf 'state:building\nstate:addressing\n'
+        core_label_rows | cut -d'|' -f1
       elif [ "$1" = pr ] && [ "$2" = list ]; then
         printf '101\n102\n'
       elif [ "$1" = pr ] && [ "$2" = view ]; then