Board Thread:Questions and Answers/@comment-27343779-20160405083111/@comment-1739368-20160405235126

Yeah, I think what separates retcons from one-time inaccuracies is consistency. Stuff like the date dio died is likely a retcon because it's used afterwards regardless of version.

The general rule of thumb is that if something is different, we check later entries of it to see if the same error is made; if so, it's likely the new canon. However, it's hard to say for the info where it's never mentioned again. This is typically why we'd enlist the use of the artbooks to set a standard, though I still don't own JoJoveller yet to confirm if any of these errors stayed.

I like what the who wiki is doing, though I'm unsure how making everything canon would sit for a manga community.