I find that people only appear in my list if you find their stats and refresh the page. A lot of mine never play anymore and so their stats dont update.
Ive found this out by using
www.bf2player.com. This site lists all of your victims and enemies, even those with less than 100global points (which bf2s doesnt do).
Find someone on your list on bf2player, then find them on bf2s and refresh the page. They will then appear.
So my guess is that maybe you kicked someones ass like 3months ago and they have just come back, updated their stats and they then appear on your page. Certainly the case with one of mine who appeared this week. I only play SF now, and have done for over a month - yet he has never even played SF.
With this, all of my victims (except my favourite) then appeared....so god knows how long ago they got their ass kicked!
I only actually remember my favourite victim...none of my other victims or enemies. He got his ass kicked in a LONG DV round which I got my 170BRS