@daria - Just checked with Memory Alpha and it looks like all First Season scripts and publicity materials referred to him as "Zimmerman." That would at least explain the first season labels. Not sure about why they did that in the second, though....
I watched some Season Four episodes later, but he didn't speak while offscreen.
Sometimes subtitles are a law unto themselves. Someone at BBC Worldwide seems to believe that Red Dwarf's use of 'holo-' (as in hologram) is actually 'hollow' (as in empty inside).
@dolari
Good question. This was toward the end of Season Two, so they surely they'd have well and truly decided they weren't going with that name by then.
And if the subtitles were coming from somewhere else, that just raises more questions!