During the musical chairs segment, we see Pig Pen standing behind a chair toward the end of the game, when Charlie Brown and Peppermint Patty are left. Pig Pen never was playing the game in the first place.
At the beginning of "Slow, Slow, Quick-Quick", Peppermint Patty invites Charlie Brown to dance by knocking his "War and Peace" book down. At the end of the number, the book has moved to the center of the room, where Charlie Brown trips over it.
Right after Peppermint Patty gets the last chair in musical chairs, we see Marcie appear in Pig Pen's place.
Charlie Brown is seen reading "War and Peace" on the porch outside the New Year's Eve party. Although we can hear him reading it normally, he is turning the pages in the wrong direction (going backwards).
When the mantle clock strikes midnight at the New Year's Eve party, we hear the first five strikes, but when the gang sings "Auld Lang Syne", we do not hear the last seven strikes.
It would have taken months for Charlie Brown to read War and Peace and the book report would have been several pages long. It is much more suitable for a college assignment.