diff --git a/lib/services/campaign-grouping-service.test.ts b/lib/services/campaign-grouping-service.test.ts
index 991c288..dcb868c 100644
--- a/lib/services/campaign-grouping-service.test.ts
+++ b/lib/services/campaign-grouping-service.test.ts
@@ -339,7 +339,7 @@ describe('groupReportIntoCampaign', () => {
     expect(callsContaining('UPDATE campaigns')).toHaveLength(0);
   });
 
-  it('re-analyzing a report already linked to a campaign that a sibling report re-matches does not increment report_count a second time', async () => {
+  it('Test G (CR-02 guard against over-firing): same-campaign re-match remains a pure no-op — the origin decrement must NOT fire when the match resolves back to the report\'s own campaign', async () => {
     // Own report is already linked to campaign-1. A SIBLING report (not this
     // report's own excluded row) also belongs to campaign-1 and matches via
     // Tier 3 (sender + subject + client). This is the CAMP-02/CR-01 gap:
@@ -464,4 +464,95 @@ describe('groupReportIntoCampaign', () => {
     });
     expect(callsContaining('INSERT INTO campaigns')).toHaveLength(1);
   });
+
+  // ===========================================================================
+  // CR-02 (gap closure, 18-05 Task 2): decrement the origin campaign's
+  // report_count on cross-campaign migration, AND on the signal-diverged
+  // create-new fall-through added by Task 1 (CR-03) above — both are the
+  // same "abandoning an origin campaign" situation, just landing on an
+  // existing sibling's campaign vs. a brand-new one. Tests E and H below
+  // FAILED against the pre-Task-2 code (confirmed during RED).
+  // ===========================================================================
+
+  it('Test E (CR-02 migration decrements origin): cross-campaign migration decrements the origin and increments the destination exactly once each', async () => {
+    stage({
+      ownReport: [{ ...REPORT_ROW, campaign_id: 'campaign-A' }],
+      ownMessage: [],
+      tier3: [{ campaign_id: 'campaign-B', title: 'Invoice Alert' }],
+    });
+
+    const result = await groupReportIntoCampaign('report-e');
+
+    expect(result).toEqual({
+      campaignId: 'campaign-B',
+      groupMethod: 'sender_subject_client',
+      created: false,
+    });
+
+    const updateCampaignCalls = callsContaining('UPDATE campaigns');
+    expect(updateCampaignCalls).toHaveLength(2);
+    const incrementCall = updateCampaignCalls.find((c) => c.sql.includes('report_count + 1'));
+    const decrementCall = updateCampaignCalls.find((c) => c.sql.includes('report_count - 1'));
+    expect(incrementCall?.params).toEqual(['campaign-B']);
+    expect(decrementCall?.params).toEqual(['campaign-A']);
+
+    const updateReportCalls = callsContaining('UPDATE reports SET campaign_id');
+    expect(updateReportCalls).toHaveLength(1);
+    expect(updateReportCalls[0].params).toEqual(['campaign-B', 'report-e']);
+  });
+
+  it('Test F (D-08 upgrade preserved, no origin to decrement): a never-grouped report upgrading to a sibling campaign increments the destination only', async () => {
+    stage({
+      ownReport: [REPORT_ROW], // campaign_id null/undefined — never grouped before
+      ownMessage: [{ id: 'own-msg-id', message_id: 'shared-message-id-upgrade' }],
+      tier1: [{ campaign_id: 'campaign-B' }],
+    });
+
+    const result = await groupReportIntoCampaign('report-f');
+
+    expect(result).toEqual({
+      campaignId: 'campaign-B',
+      groupMethod: 'message_id',
+      created: false,
+    });
+
+    const updateCampaignCalls = callsContaining('UPDATE campaigns');
+    expect(updateCampaignCalls).toHaveLength(1);
+    expect(updateCampaignCalls[0].sql).toContain('report_count + 1');
+    expect(updateCampaignCalls[0].params).toEqual(['campaign-B']);
+
+    const updateReportCalls = callsContaining('UPDATE reports SET campaign_id');
+    expect(updateReportCalls).toHaveLength(1);
+    expect(updateReportCalls[0].params).toEqual(['campaign-B', 'report-f']);
+  });
+
+  it('Test H (plan-checker-flagged divergence case): signal-diverged create-new also decrements the abandoned origin campaign exactly once', async () => {
+    stage({
+      ownReport: [{ ...REPORT_ROW, campaign_id: 'campaign-A' }],
+      ownMessage: [],
+      tier3: [],
+      ownCampaign: [
+        { campaign_key: 'sender_subject_client:5:old subject:10', group_method: 'sender_subject_client' },
+      ],
+      insertCampaign: [{ id: 'diverged-new-campaign-h' }],
+    });
+
+    const result = await groupReportIntoCampaign('report-h');
+
+    expect(result).toEqual({
+      campaignId: 'diverged-new-campaign-h',
+      groupMethod: 'sender_subject_client',
+      created: true,
+    });
+
+    expect(callsContaining('INSERT INTO campaigns')).toHaveLength(1);
+    const updateCampaignCalls = callsContaining('UPDATE campaigns');
+    expect(updateCampaignCalls).toHaveLength(1);
+    expect(updateCampaignCalls[0].sql).toContain('report_count - 1');
+    expect(updateCampaignCalls[0].params).toEqual(['campaign-A']);
+
+    const updateReportCalls = callsContaining('UPDATE reports SET campaign_id');
+    expect(updateReportCalls).toHaveLength(1);
+    expect(updateReportCalls[0].params).toEqual(['diverged-new-campaign-h', 'report-h']);
+  });
 });
diff --git a/lib/services/campaign-grouping-service.ts b/lib/services/campaign-grouping-service.ts
index 84ea7b9..e11a59d 100644
--- a/lib/services/campaign-grouping-service.ts
+++ b/lib/services/campaign-grouping-service.ts
@@ -20,6 +20,7 @@
  * Tier 3 (sender + normalized subject + client + 24h window).
  */
 
+import type { PoolClient } from 'pg';
 import { postgresClient } from './postgres-client';
 
 // =============================================================================
@@ -118,6 +119,24 @@ function computeTier3Key(
   return `sender_subject_client:${requesterContactId}:${normalizedSubject}:${companyId}`;
 }
 
+/**
+ * CR-02: decrements a now-abandoned origin campaign's report_count. Shared
+ * by both places a report can be abandoned from its origin campaign — the
+ * sibling-migration branch (moving to a DIFFERENT existing campaign) and the
+ * signal-diverged create-new fall-through (moving to a brand-new campaign) —
+ * so neither is left with a stale, inflated count. Decrement only; never
+ * deletes the origin row even if its count reaches 0 (out of scope — see
+ * CR-02 scope note at the call sites).
+ */
+async function decrementOriginCampaign(client: PoolClient, originCampaignId: string): Promise<void> {
+  await client.query(
+    `UPDATE campaigns
+        SET report_count = report_count - 1, updated_at = NOW()
+      WHERE id = $1`,
+    [originCampaignId]
+  );
+}
+
 /**
  * Shared entry point called by the webhook path, the cron sweep, and the
  * on-demand `/analyze` route. Looks up the report's own signal (message,
@@ -363,6 +382,17 @@ export async function groupReportIntoCampaign(
           `UPDATE reports SET campaign_id = $1, updated_at = NOW() WHERE id = $2`,
           [matchCampaignId, reportId]
         );
+        // CR-02: if the report had a DIFFERENT prior campaign (the
+        // same-campaign case returned above; a never-grouped report has no
+        // origin — D-08), decrement it so it doesn't keep a permanently
+        // stale report_count for a report it no longer holds. Scope:
+        // decrement only, never delete the origin row even if its count
+        // reaches 0 (deleting introduces FK-cascade/detail-route risk out of
+        // scope for this gap fix; an empty campaign is a strictly lesser
+        // problem than a stale count).
+        if (ownReport.campaign_id) {
+          await decrementOriginCampaign(client, ownReport.campaign_id);
+        }
         return { campaignId: matchCampaignId, groupMethod: matchGroupMethod, created: false };
       }
 
@@ -397,10 +427,14 @@ export async function groupReportIntoCampaign(
             created: false,
           };
         }
-        // Own campaign row is gone, or the report's signal has genuinely
-        // diverged from its stored key — fall through to create-new below.
-        // (CR-02: decrementing this now-abandoned origin campaign's
-        // report_count is handled in Task 2 of the 18-05 gap-closure plan.)
+        // CR-02: own campaign row is gone, or the report's signal has
+        // genuinely diverged from its stored key — this report is about to
+        // be abandoned from its origin campaign in favor of a brand-new one
+        // below (the same class of abandonment as the sibling-migration
+        // branch above, just landing on a new row instead of an existing
+        // sibling's). Decrement now so the origin doesn't show a stale
+        // count. Falls through to create-new unchanged.
+        await decrementOriginCampaign(client, ownReport.campaign_id);
       }
 
       // No match on any tier — create a new campaign. Prefer the strongest