Well I've noted before that the end of the year special for 2005 has never been subbed. Well if you watch the previews for the episode 291 from what I've seen it's a continuation of the 2005 special. This makes it even more apparient that someone could have subbed it by now, earlier this year I checked out the torrent and easily downloaded it. So all I can come to is that it was overlooked do to the rush and stress of other immediate episodes which at the time were in much more demand.
If you spoiler me, I will eat you with tater tots.