Buffy doesn't actually sound like a real first name. For argument's sake, if her first name were Elizabeth, her friends could have gone with Buffy because that's what they called her. On the other hand, if that were the case, I don't think they'd have put her middle name in.

I imagine Anne's on the headstone because Joss wanted a middle name for her to be using at the start of season 3. She may have had no middle name before then.

Oh, I think being good at denial is a human trait. Or maybe that's just my excuse because I'm so good at it. ;-)