I find that BC times in Wikidata are usually 1 year ahead of the real year.
Rome is founded in 753 BC, but Wikidata says 752 BC
Cleopatra died in 30 BC, but Wikidata says 29 BC
but, there are correct ones, for example,
the birth date and death date of Virgil (Q1398) is correct.
I guess this has something to do with internal Georgian Calendar used by Wikidata, which says year 0 should be 1 BC, and year -1 should be 2 BC. And perhaps programmers didn't handle this very well when importing data.