I recently stumbled across an old meta discussion in which some people suggested that history of mathematics questions were off-topic for MO. This took me by surprise and I would like to ask for clarification about what kinds of "history" questions are unwelcome (by some). After all, "Has this result been proved before?" is technically a history question. In the aforementioned discussion, some people seemed to argue that the correctness of an answer to a historical question may require professional historical training to assess, and that MO readers typically don't have that training. I don't want to get into a long discussion here about why I believe this argument to be bogus (and founded on a misconception of what professional historical research is about), but will just say that the historical questions I have seen on MO have, in my opinion, either been on-target for the MO audience, or else defective for readily identifiable reasons other than a blanket inappropriateness of all history questions.
In short, my view is that history questions are fair game. I'd like to know if I should adjust my view.