diff --git a/src/undate/undate.py b/src/undate/undate.py
index 4539924..aeed091 100644
--- a/src/undate/undate.py
+++ b/src/undate/undate.py
@@ -247,11 +247,9 @@ def __contains__(self, other: "Undate") -> bool:
         return (
             self.earliest <= other.earliest
             and self.latest >= other.latest
-            # precision is not sufficient for comparing partially known dates
+            # is precision sufficient for comparing partially known dates?
             and self.precision > other.precision
         )
-        # TODO: how to compare partially unknown values
-        # like 19xx and 199x or 1801-XX and 1801-1X
 
     @property
     def known_year(self) -> bool:
diff --git a/tests/test_undate.py b/tests/test_undate.py
index ba1d6fe..210419f 100644
--- a/tests/test_undate.py
+++ b/tests/test_undate.py
@@ -214,8 +214,6 @@ def test_lt_notimplemented(self):
         (Undate(2022, 1, 1), Undate(2022)),
         (Undate(2022, 12, 31), Undate(2022)),
         (Undate(2022, 6, 15), Undate(2022, 6)),
-        # TODO: support partially known dates that are unambiguously in range
-        # (Undate("199X"), Undate("19XX")),
     ]
 
     @pytest.mark.parametrize("date1,date2", testdata_contains)
@@ -227,26 +225,23 @@ def test_contains(self, date1, date2):
         (Undate(1980), Undate(2020)),
         (Undate(1980), Undate(2020, 6)),
         (Undate(1980, 6), Undate(2020, 6)),
+        # partially known dates that are similar but same precision,
+        # so one does not contain the other
+        (Undate("199X"), Undate("19XX")),
+        # - specific month to unknown month
+        (Undate(1980, 6), Undate(1980, "XX")),
+        # some of these might overlap, but we don't have enough
+        # information to determine
+        # - unknown month to unknown month
+        (Undate(1980, "XX"), Undate(1980, "XX")),
+        # - partially unknown month to unknown month
+        (Undate(1801, "1X"), Undate(1801, "XX")),
     ]
 
     @pytest.mark.parametrize("date1,date2", testdata_not_contains)
     def test_not_contains(self, date1, date2):
         assert date1 not in date2
 
-    def test_contains_ambiguous(self):
-        # date not in range due to precision
-        # TODO: can we return an unknown instead of false?
-        # or should this raise a not implemented error?
-
-        # these are cases where dates *might* overlap,
-        #  but we don't have enough information to determine
-        # - specific month to unknown month
-        assert Undate(1980, 6) not in Undate(1980, "XX")
-        # - unknown month to unknown month
-        assert Undate(1980, "XX") not in Undate(1980, "XX")
-        assert Undate(1980, 6) not in Undate(1980, "XX")
-        assert Undate(1801, "1X") not in Undate(1801, "XX")
-
     def test_sorting(self):
         # sorting should be possible based on gt/lt
         # test simple cases for sorting