I don't think I've ever not tagged someone who's tagged an EP of mine. I know that I have a horrible, horrible tendency to drop threads but that's because I can fail at remembering things sometimes and my brain is iffy when it comes to slows, but I try, really. (This is also a 'if you need a tag, give me a nudge, I won't be offended by the nudge, honest' warning.)

I second Wiki and Google as being your friend.

As for tagging out, I try to tag Doc out as much as I can and there are still some pups that I'd love to have him thread with but I'm just waiting for the right moment or time. It's not an 'I don't know your canon' thing at all, it's just a 'do I have the brainpower for another thread'.