Many of the crowd/ group scenes in that special have characters who switch positions.
For the closing christmas medley, there are two rooms where characters are at. Some characters appear in both rooms. These characters include Statler, waldorf (although they both appear on the end side of both rooms), a female anything muppet (Does she have a name? he had brown hair and a red shirt), Simon Soundman, The Turkey, and Camillia. Also, when Gonzos on the hanger, he wears pajamas, and when singing in the medley, he's dressed up (Kermit was the only other character who was dressed differently from how he dressed for the rest of the special), and beaker doesn't appear untill it's his turn to sing (which is halfway through the scene). Also, Animal is not the only major character not there. Zoot and herry monster were not in that scene.
When the Sesame Street cast sings deck the halls, Biff and Sully change shots. Whenever the shot has half of the singers, Biff and Sully are closer to Big Bird in the shots that have big bird, but in the shots with bert and Ernie, Biff is up the hill while Sully is behind sherlock hemlock and others who are right behind ernie and bert.
In the opening song, Rizzo changes spots. In wide shots, he is sitting right next to Lips (probably so that Steve Whitmire can perform both characters at once), but near the end of the song, Rizzo is with the other rats at a different part of the truck.
There are also many characters who were not shown with the main cast at the begining whose arrivals were not announced or acknowledged. Besides The newsman, we eventually see Bobby Benson, a Muppaphone, Link Hogthrob, Foo Foo (although not with Piggy), and Nigel The Conductor. We never see them enter, and they were not in the truck at the beginning (althouhg I guess the muppaphone could have been in the truck, since he is small enouhg to maybe not be seen).