diff --git a/fiftyone_pipeline_did/readme.md b/fiftyone_pipeline_did/readme.md
index d0a80d9..c0ea2b9 100644
--- a/fiftyone_pipeline_did/readme.md
+++ b/fiftyone_pipeline_did/readme.md
@@ -154,7 +154,7 @@ same whichever language parsed the bytes.
 | `UNEXPECTED_END` | The data stopped in the middle of an envelope field |
 | `INVALID_DOMAIN_ENCODING` | The creator domain is not terminated or is longer than the OWID maximum |
 | `BYTE_COUNT_MISMATCH` | The declared payload length disagrees with the bytes present |
-| `IMPLEMENTATION_CAPACITY_EXCEEDED` | The envelope is consistent but larger than this runtime can hold |
+| `IMPLEMENTATION_CAPACITY_EXCEEDED` | The envelope is consistent but larger than this runtime can hold, or dated past the end of the year 9999 where `datetime` stops. The four byte minute count runs to 15 February 10186, and the read answers with this status rather than raising on such a count |
 | `ABSENT_NODE` | The version 0 marker, which stands for an absent envelope |
 | `MALFORMED_ENVELOPE` | Malformed in a way none of the above describes |
 | `PAYLOAD_TOO_SHORT` | The envelope was read but the payload is shorter than the 5 byte header, so the type cannot be read |
diff --git a/fiftyone_pipeline_did/src/fiftyone_pipeline_did/fod_id.py b/fiftyone_pipeline_did/src/fiftyone_pipeline_did/fod_id.py
index 57190df..4232d49 100644
--- a/fiftyone_pipeline_did/src/fiftyone_pipeline_did/fod_id.py
+++ b/fiftyone_pipeline_did/src/fiftyone_pipeline_did/fod_id.py
@@ -79,7 +79,13 @@ class FodIdParseStatus(Enum):
     INVALID_DOMAIN_ENCODING = "InvalidDomainEncoding"
     #: The declared payload byte count disagrees with the bytes present.
     BYTE_COUNT_MISMATCH = "ByteCountMismatch"
-    #: The envelope is consistent but larger than this runtime can hold.
+    #: The envelope is consistent but larger than this runtime can hold, or
+    #: dated past the end of the year 9999 where ``datetime`` stops. The
+    #: four byte minute count of OWID versions 2 and 3 runs to 15 February
+    #: 10186, and the OWID reader judges the count before the arithmetic,
+    #: so a read answers with this status rather than raising. The same
+    #: bytes read fine where the date type is wider, so the status is not a
+    #: fault in the data.
     IMPLEMENTATION_CAPACITY_EXCEEDED = "ImplementationCapacityExceeded"
     #: The version 0 marker, which stands for an absent envelope and never
     #: produces a value.
diff --git a/fiftyone_pipeline_did/tests/test_fodid.py b/fiftyone_pipeline_did/tests/test_fodid.py
index 048c3be..d2c840b 100644
--- a/fiftyone_pipeline_did/tests/test_fodid.py
+++ b/fiftyone_pipeline_did/tests/test_fodid.py
@@ -605,6 +605,51 @@ def test_wrong_input_type_reports_invalid_input_type(self):
         self.assert_failed(FodId.try_from_byte_array("AwB="),
                            FodIdParseStatus.INVALID_INPUT_TYPE)
 
+    # ----- A date the runtime cannot hold -----
+
+    def _dated_past_the_year_9999(self):
+        """A signed envelope whose four byte minute count is 0xFFFFFFFF,
+        which the wire format allows and which lands on 15 February 10186,
+        past the end of the year 9999 where ``datetime`` stops. The bytes
+        are changed after signing, which is fine because the read refuses
+        the date before any signature is looked at."""
+        raw = bytearray(self.factory.signed_bytes(canonical_payload()))
+        # The four little endian date bytes sit after the version byte, the
+        # domain and its terminator.
+        at = 1 + raw.index(0, 1) + 1
+        raw[at:at + 4] = bytes([0xFF] * 4)
+        return bytes(raw)
+
+    def test_date_past_the_year_9999_is_implementation_capacity_exceeded(
+            self):
+        # The OWID reader judges the count before the arithmetic, so the
+        # read answers with a status instead of raising OverflowError, and
+        # the 51Did surface carries that status through unchanged on both
+        # the byte and the base64 surface. The same bytes read fine where
+        # the date type is wider, so the status is the runtime's limit and
+        # not a fault in the data.
+        raw = self._dated_past_the_year_9999()
+        self.assertIs(ParseStatus.IMPLEMENTATION_CAPACITY_EXCEEDED,
+                      Owid.parse_bytes(raw).status)
+        self.assert_failed(
+            FodId.try_from_byte_array(raw),
+            FodIdParseStatus.IMPLEMENTATION_CAPACITY_EXCEEDED)
+        self.assert_failed(
+            FodId.try_from_base64(base64.b64encode(raw).decode()),
+            FodIdParseStatus.IMPLEMENTATION_CAPACITY_EXCEEDED)
+
+    def test_raising_readers_name_the_date_the_runtime_cannot_hold(self):
+        # The raising readers run the same walk, so the date is the
+        # documented OwidError with the status in the message, never the
+        # OverflowError the arithmetic would have raised.
+        raw = self._dated_past_the_year_9999()
+        with self.assertRaises(OwidError) as raised:
+            FodId.from_base64(base64.b64encode(raw).decode())
+        self.assertIn("ImplementationCapacityExceeded", str(raised.exception))
+        with self.assertRaises(OwidError) as raised:
+            FodId.from_byte_array(raw)
+        self.assertIn("ImplementationCapacityExceeded", str(raised.exception))
+
     # ----- Parsing and verifying are separate -----
 
     def test_tampered_signature_parses_then_verifies_as_invalid(self):
diff --git a/owid-python b/owid-python
index 0944322..0a77e39 160000
--- a/owid-python
+++ b/owid-python
@@ -1 +1 @@
-Subproject commit 09443229f98f81bd1cedc624eec74f9486b9042d
+Subproject commit 0a77e39e02151ebc477b19b67c6a6c0f4f317a1b