When Barney and his girlfriend are at the bar and turn to leave, Barney says "don't wait up" and in the next shot he's walking out and his girlfriend disappeared.
It is well-established that Barney has a 300-inch television on the wall facing his living room couch, yet when he takes Nora to his apartment we see the wall and instead of a giant television there is a fireplace and bookshelves.
In the letter Weird Al receives from young Ted on February 21, 1985, the letter says that he is 8 years old. In previous episodes it is confirmed that he was born in April of 1978, so the letter should be saying that he is 6 going on 7.