Have you ever accidentally necroposted?

I wasn't sure how to answer this, because I've never been the one that started it.
Like a lot of others, I've commented on threads when someone else already did it and it popped up in current discussions. I just browse through discussions and comment on the ones that look interesting, I don't generally look through the dates. Just this past week I had commented on a thread and the next post was a mod commenting that it was necroposted and closing it. I've often wondered why they don't just automatically close threads that are past a certain age, then necroposting couldn't happen.