Pleased as I am to get back onto the second column of the rep count, there's a mismatch between José Figueroa-O'Farrill's reported rep (7992) and the reputation on his reputation graph (over 8000).

That's pretty weird. I guess it's possible that a batch of suspicious-looking votes was thrown out, but you would probably have noticed a single person voting up each of your old posts in quick succession. Somebody reported a similar problem on meta.SO: http://meta.stackoverflow.com/questions/37109/reputation-graph-level-is-lower-than-actual. Do you want me to try triggering a rep recalc? I don't know if it will help.

how can you see whether it is the same person voting up the posts?

You can't, but if you see that a bunch of your post were each voted on once in a short period of time, that's a strong hint that a single person is going through your profile voting on all your old posts. There's nothing wrong with that, but if (for example) the votes are in very quick succession (indicating that the person isn't reading the posts) and if the user votes only on your posts and not anybody else's, then the software may decide that some kind of sock-puppetry or other abuse of the voting system is going on.