John F. Kennedy Jr. is heard speaking with the typical Kennedy Boston accent. In real life, John Kennedy Jr. spent virtually his entire life in New York and had no traces of a Boston accent whatsoever.
When Kramer leaves the auditions to find the bathroom down the hall, the Law & Order (1990) poster on the wall reads backwards. Presumably the shot was reversed to be consistent with Stu Shermack's directions of "on the right at the very end."
When George is complaining that he won't get his lab results back for another two days and is exiting the bathroom, Jerry is sitting on the chair pretending to read the script with pink binding and it's clear the pages are all blank.
When the exterior of the coffee shop is shown at 19:56 you can see that it says Tom's Restaurant.
When George is on the phone with his doctor at the pilot taping, there is a folded up Directors chair behind him with the name "Michael Richards" on it. If it was meant to be in the scene as "a chair on a stage" Michael Richards wouldn't exist in the story.
Russel is obsessed with Elaine and doesn't know she is friends with Jerry. However, there is a character in the pilot named Elaine Benes. Russel doesn't seem to make a connection between the Elaine Benes he knows and the Elaine Benes in the pilot.