http://www.manic-expression.com/another-look-at-retcons-in-sitcoms-and-trek/

Friends

Yeah I know as I mentioned I covered a bunch of these last tine. Here’s a fun one I missed. The problem with birthdays. Ok first Ross says he is 29 three times over three seasons. Sure that makes sense. The biggest problem however comes with the episode “The One Where They All Turn 30”. This episode aired in season 7. It’s Rachel’s birthday, even though in season 3 Chandler clearly says that Rachel is 29. While the rest of the birthday’s are flashback most of the timeline’s don't add up. The worst is Monica who says she is 26 in Season One. The flashback to her 30th she and Chandler are living together and her parent know so that would put it at Season 6. She should have been 30 back in Season 4! Birth dates were an issue, was Ross born in January or not? And Phoebe’s birthday was on Halloween one episode even though there no indication of that in either the Halloween episode the year before or the episode where they celebrated Phoebe’s birthday (set in Feb!) in Season 1. I could be here all day.

http://www.manic-expression.com/another-look-at-retcons-in-sitcoms-and-trek/


I have found inconsistencies like this in many different shows. In my opinion, the "Flintstones" is the worst offender in this department. "The Golden Girls" is a close second. I have even found some of these types of inconsistencies on "Sesame Street".