Let's list the flaws and inconsistencies within the show
I'll start with a few off the top of my head
1. In the season 1 episode "The Alliance" we learn that Meredith is an accountant. After season 1, she obviously isn't an accountant.
2. Again in "The Alliance" we learn that Meredith's birthday is the firth birthday coming up but it's not for about a month, or a few weeks or something. Then in season 4, when Jim is put in charge of the office for the day we learn that it's birthday month. There are 3 birthday's in one month ending with Meredith's. And speaking of Birthdays
3. Wow, "The Alliance" is just causing a lot of problems here. We kind of get the impression from that episode that they never really did birthday parties in the office. Michael just wanted to do something special to lift the spirits of his employees. Then in Season 4 we get a montage of Michael surprising employees on their birthday's and it's implied that this is what Michael has always done. I guess it's possible that he only began the birthday tradition after season 1, but I don't think that was the implication.
4. Pam and volleyball. In Season 4 we learn that she always faked PMS to get out of playing sports in gym including volleyball. Then in season 5 we learn that she played volleyball in high school and college and went to volleyball camp most summers.
What else do we have?
https://www.youtube.com/watch?v=4FE9SLJ2Xoc