Continuity mistake: Kelly said her youngest brother can burp his whole name Kenneth Leonard Kapowski in one burp. However in the previous year, Kelly had an infant brother named Billy. According to this info, unlikely Kenneth would be younger than Billy.
Factual error: When Zack is given the old newspaper with Mr. Belding's article, the headline reads, "Picture on pages 3 and 4." When he looks at the picture, he looks at the middle of the paper, with quite a few pages at both sides of the newspaper. Pages 3 and 4 would be near the front and would be on opposite sides of the same page.
Continuity mistake: In this episode, Screech's mother kisses her Elvis statue before her trip while it is facing towards the right; indicating that this is the correct way that is should be facing. However, when she comes home after her trip the "new" statue is facing the same direction; right. She complains and says that the statue should always face towards the kitchen so he can see her cook; which is towards the left.
Plot hole: After the meeting with Zack's "fake Dad", Mr. Belding informs Zack he wrote a letter to see the Dad again... However when the "real" Dad sees the fake "Belding" (whom the Dad didn't know was fake), the Dad never questioned about the "seeing him AGAIN" letter when this real Dad never met Belding before. In addition, wouldn't the Dad question this letter to Zack anyway?
Other mistake: In the scene where the Glee Club is discussing that Violet will win them the contest, Violet leaves as she is upset about Screech. Zack then comments about "No one having a voice like Violet's". If you look at Mr. Tuttle, he mouths the words that Zack says.
Revealing mistake: When they are reading the reviews in the newspaper, look at the back page. It's the sports section. Next when Jessie comes back to Zack and tells him what Mr Belding was hiding, she says the paper is from 1968. But look at the back of that paper also. They are using the exact same paper. The reviews and the 1968 paper are the exact same.