diff --git a/datatypes/epc/domain/tests/test_from_sap_schema.py b/datatypes/epc/domain/tests/test_from_sap_schema.py
index d05b7d78c..dd8f021dd 100644
--- a/datatypes/epc/domain/tests/test_from_sap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_sap_schema.py
@@ -78,6 +78,24 @@ class TestFromSapSchema17_1Tracer:
         assert result.total_floor_area_m2 == 68.0
 
 
+class TestFromSapSchema17_1RebaselineFields:
+    """The calc-affecting categoricals the WIP mapper dropped (ADR-0037). Their
+    absence left the full-SAP family un-rebaselined and mis-scored, producing the
+    portfolio-796 "impossible downgrade"."""
+
+    def test_maps_sap_version_so_pre_sap10_rebaseline_can_fire(self) -> None:
+        # The full-SAP family lodges SAP 2012 (sap_version 9.92). Without it on
+        # the EpcPropertyData, CalculatorRebaseliner cannot fire trigger (a)
+        # (`sap_version < 10.2` → Effective = Calculated), so Effective
+        # Performance wrongly stays equal to the lodged SAP-2012 score while the
+        # plan models the SAP-10.2 calc — the impossible downgrade.
+        schema = from_dict(SapSchema17_1, load("sap_17_1.json"))
+
+        result = EpcPropertyDataMapper.from_sap_schema_17_1(schema)
+
+        assert result.sap_version == 9.92
+
+
 class TestFullSapHasHotWaterCylinderFallback:
     """Some full-SAP certs (e.g. SAP-Schema-17.0 cert 8265-7433-3220-9736-7902)
     omit the top-level `has_hot_water_cylinder` and lodge it only under