Also, Herbert Birdsfoot doesn't appear in A Muppet Family Christmas. It's much easier to see who all is in the various crowd scenes in that speical than in The Muppet Movie finale. Also, while TMM featured nearly every Henson creation, and while it would be appropriate for The Mupepts: A Celebration of 30 Years to have doen the same, I think that MFC just featured Sesame Street characters who were currently active on the show at the time.
I don't think Herbert is in the 30th anniversary special. While that special even brought back some Sam and Friends characters (something TMM didn't do at the end), I think this special also only featured SS characters who were currently on the show, and not any characters who hadn't been in new material in a long time (I think it would have been appropriate to have had Herbert Birdsfoot, Roosevelt Franklin and his mother, Lefty, Harvey Kneeslapper, The Mudman, Rodeo Rosie, and Professor Hastings in that special).