I do remember, however, that in Buffy just initials were used often.

I think that's one of those conventions that varies from fandom to fandom. You don't get much more old-skool slash than Original Trek, and they use single letters pretty commonly (K/S). Same with Blakes' 7. I was a little confused by that when I moved from Blakes to popslash, but I pretty quickly realised that using just initials really wouldn't work in another fandom where everyone's a J. :-)