diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index 520bb9207..f9e9c02a7 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -96,8 +96,9 @@ shared `area` argument (place name, bounding box, or point and radius) and cap
 lists at 25 rows by default. `aircraft_in_area` and `vessels_in_area` can also
 count every match by a field (`group_by`: operator, country or type for
 aircraft; type or destination for ships; the ten largest groups, then other and
-unknown counts) and summarize airborne altitude and speed (`stats`: count, min,
-median, mean, max). Both cover all matches, not just the rows returned. Voice offers the same queries next to its app
+unknown counts; the summary says when a feed reports none of the field) and
+summarize airborne altitude and speed (`stats`: count, min, median, mean, max).
+Both cover all matches, not just the rows returned. Voice offers the same queries next to its app
 actions: the session lists them, and the browser runs them through the same
 catalog, loaded on first use. See [tools and the MCP server](TOOLS.md).
 
diff --git a/src/tools/queries/aviation.js b/src/tools/queries/aviation.js
index e3aca82c4..23652f211 100644
--- a/src/tools/queries/aviation.js
+++ b/src/tools/queries/aviation.js
@@ -105,7 +105,9 @@ export const aircraftInArea = defineTool({
       group_by: {
         type: 'string',
         enum: Object.keys(GROUP_LABELS),
-        description: 'Count matched aircraft by this field, largest first.',
+        description:
+          'Count matched aircraft by this field, largest first. Feeds that do not ' +
+          'report the field count those aircraft as unknown.',
       },
       stats: {
         type: 'boolean',
diff --git a/src/tools/queries/aviation.test.mjs b/src/tools/queries/aviation.test.mjs
index 618085b00..b6b6e3497 100644
--- a/src/tools/queries/aviation.test.mjs
+++ b/src/tools/queries/aviation.test.mjs
@@ -409,7 +409,7 @@ test('aircraft in an area can be counted by operator over every match', async ()
   });
   assert.equal(
     result.summary,
-    '4 aircraft in 60 km around 37.600, -122.300; most by operator: United (2), Delta (1).',
+    '4 aircraft in 60 km around 37.600, -122.300; most by operator: United (2), Delta (1); 1 unknown.',
   );
   assert.equal(result.data.returned, 1);
   assert.deepEqual(result.data.breakdown, {
diff --git a/src/tools/queries/maritime.test.mjs b/src/tools/queries/maritime.test.mjs
index d1c43e60a..662e5bdf2 100644
--- a/src/tools/queries/maritime.test.mjs
+++ b/src/tools/queries/maritime.test.mjs
@@ -237,7 +237,7 @@ test('vessels in an area can be counted by destination with a speed summary', as
   });
   assert.equal(
     result.summary,
-    '2 vessels in 20 km around 37.780, -122.400; most by destination: OAKLAND (1).',
+    '2 vessels in 20 km around 37.780, -122.400; most by destination: OAKLAND (1); 1 unknown.',
   );
   assert.deepEqual(result.data.breakdown, {
     field: 'destination',
diff --git a/src/tools/results.js b/src/tools/results.js
index b4a24c72a..528f59ea5 100644
--- a/src/tools/results.js
+++ b/src/tools/results.js
@@ -78,13 +78,20 @@ export function numericSummary(rows, field) {
   };
 }
 
-/** "; most by operator: Delta (12), United (9), American (7)" or "". */
+/**
+ * "; most by operator: Delta (12), United (9), American (7); 4 unknown", or
+ * "; no operator reported" when no row carries the field.
+ */
 export function breakdownPhrase(result, label) {
-  if (!result.groups.length) return '';
+  if (!result.groups.length)
+    return result.unknown_count ? `; no ${label} reported` : '';
   const top = result.groups
     .slice(0, 3)
     .map((group) => `${group.value} (${group.count})`);
-  return `; most by ${label}: ${top.join(', ')}`;
+  const unknown = result.unknown_count
+    ? `; ${result.unknown_count} unknown`
+    : '';
+  return `; most by ${label}: ${top.join(', ')}${unknown}`;
 }
 
 function sum(values) {
diff --git a/src/tools/results.test.mjs b/src/tools/results.test.mjs
index ba67b9f64..2e480afcd 100644
--- a/src/tools/results.test.mjs
+++ b/src/tools/results.test.mjs
@@ -63,6 +63,7 @@ test('a numeric summary skips missing values', () => {
 
 test('the breakdown phrase names the three largest groups', () => {
   const result = {
+    unknown_count: 0,
     groups: [
       { value: 'A', count: 4 },
       { value: 'B', count: 3 },
@@ -74,5 +75,14 @@ test('the breakdown phrase names the three largest groups', () => {
     breakdownPhrase(result, 'type'),
     '; most by type: A (4), B (3), C (2)',
   );
-  assert.equal(breakdownPhrase({ groups: [] }, 'type'), '');
+  assert.equal(
+    breakdownPhrase({ ...result, unknown_count: 5 }, 'type'),
+    '; most by type: A (4), B (3), C (2); 5 unknown',
+  );
+  // A feed that never reports the field says so instead of staying silent.
+  assert.equal(
+    breakdownPhrase({ groups: [], unknown_count: 236 }, 'operator'),
+    '; no operator reported',
+  );
+  assert.equal(breakdownPhrase({ groups: [], unknown_count: 0 }, 'type'), '');
 });