We help the helpless (fanfic writer)

I think, if I know canon made a mistake and correcting it in fic won't detract from the story or break canon, too much, I'll correct it.

But writing in any historical fandom, it's a case of 'does it work to be historically correct, or not?' For example, if I were to write a fic about Sharpe, set immediately after the novel Sharpe's Company, I would have to stick with canon because the author fudged history to make his canon work.