diff --git a/etl/hubspot/hubspot_deal_differ.py b/etl/hubspot/hubspot_deal_differ.py
index 967a8de5b..46de2314d 100644
--- a/etl/hubspot/hubspot_deal_differ.py
+++ b/etl/hubspot/hubspot_deal_differ.py
@@ -268,8 +268,8 @@ class HubspotDealDiffer:
             ),
             "confirmed_survey_time": new_deal.get("confirmed_survey_time"),
             # Carried for the log/amend flows: sent to OpenHousing as the
-            # bookable resource, falling back to the configured default
-            # surveyor when absent.
+            # bookable resource. Mandatory for those flows — a deal without
+            # it fails the message contract's validation and dead-letters.
             "third_party_surveyor_identifier": new_deal.get(
                 "third_party_surveyor_identifier"
             ),
diff --git a/tests/orchestration/test_abri_orchestrator_amend_job.py b/tests/orchestration/test_abri_orchestrator_amend_job.py
index 1fb4fef12..86198ca48 100644
--- a/tests/orchestration/test_abri_orchestrator_amend_job.py
+++ b/tests/orchestration/test_abri_orchestrator_amend_job.py
@@ -126,8 +126,8 @@ def test_amend_job_books_the_deals_third_party_surveyor_as_the_resource(
     mock_session: MagicMock,
     deal_database: FakeDealDatabase,
 ) -> None:
-    # Arrange: a deal carrying a third-party surveyor identifier amends the
-    # appointment against that resource instead of the configured default.
+    # Arrange: the deal's third-party surveyor identifier is booked as the
+    # amended appointment's resource.
     deal_database.job_nos[DEAL_ID] = JOB_NO
     mock_session.post.return_value.content = _load_fixture(
         "abri_relay_amendoptiappt_success_response.xml"
diff --git a/tests/orchestration/test_abri_orchestrator_log_job.py b/tests/orchestration/test_abri_orchestrator_log_job.py
index 86d22211e..0e8dbdd0b 100644
--- a/tests/orchestration/test_abri_orchestrator_log_job.py
+++ b/tests/orchestration/test_abri_orchestrator_log_job.py
@@ -145,8 +145,8 @@ def test_log_job_sends_a_logjob_envelope_built_from_the_deals_fields(
 def test_log_job_books_the_deals_third_party_surveyor_as_the_resource(
     orchestrator: AbriOrchestrator, mock_session: MagicMock
 ) -> None:
-    # Arrange: a deal carrying a third-party surveyor identifier books the
-    # job against that resource instead of the configured default surveyor.
+    # Arrange: the deal's third-party surveyor identifier is booked as the
+    # job's resource.
     mock_session.post.return_value.content = _load_fixture(
         "abri_relay_logjob_success_response.xml"
     )