User interface currently displays "14 February 1 BCE" for the date shown in a [https://www.wikidata.org/w/index.php?title=Q4115189&type=revision&diff=252106455&oldid=252106367 diff] as "−0001-02-14T00:00:00" But the user interface displays "14 February 0" for the date shown in [https://www.wikidata.org/w/index.php?title=Q4115189&diff=prev&oldid=252085424 another diff] as "+0000-02-14T00:00:00".
The first example is wrong because the year −0001 (or −1) is supposed to be 2 BCE according to [[MediaWikiWiki:Wikibase/DataModel#Dates and times]].
The second example is wrong because years greater than or equal to 1 are displayed without a suffix (no CE, AD, etc.) So this implies that 0 must be CE, since it also lacks a suffix. But all authorities that use 0 and negative years regard the year 0 to be equivalent to 1 BCE. No authority recognizes 0 CE.
This bug should be fixed in conjunction with T94064, "Date of +0000-01-01 is allowed but undefined in wikibase but is not allowed in xsd:dateTime as implemented by blazegraph".