API allow to add wrong date values for day and month precision. For example:
+2003-12-00T00:00:00Z with precision = DAY
+2003-00-00T00:00:00Z with precision = MONTH
The values can not be displayed correctly by Wikidata UI.
See P577 value at page as example:
https://www.wikidata.org/w/index.php?title=Q4115189&oldid=1485553016
I fixed such wrong values. But its are created again and again by different users.
See the next discussions as examples:
https://www.wikidata.org/wiki/User_talk:Rdmpage#Date_format
https://www.wikidata.org/wiki/User_talk:Csisc#Corrupted_dates
**Steps to reproduce**
1. Go to https://www.wikidata.org/wiki/Special:ApiSandbox
2. Set action = wbcreateclaim
3. entity = Q4115189
4. snaktype = value
5. property = P577
6. value = {"time": "+2003-12-00T00:00:00Z", "precision": 11, "timezone": 0, "before": 0, "after": 0, "calendarmodel": "http://www.wikidata.org/entity/Q1985727"}
7. token -> click autofill
8. Execute request
**Actual behavior**
Wrong claim is successfully created.
**Expected behavior**
The API call should fail with invalid-snak code. The claim should not be created. Behavior should be the same as for other wrong date values, for example for "+2003-99-99T00:00:00Z".
Note: maybe I created the same issue several years ago, but I failed to find it.