Launch Party - S4-E3
Continuity mistake: In 2-13 "The Secret" Pam and Jim are talking about how Jim used to have a crush on Pam when she first started here. This implies that Jim was working here when Pam was hired. However, in this episode Pam says that when Jim first started working there she said, "Enjoy this moment, because you're never going to go back to this time before you met your desk-mate, Dwight." These two scenes contradict each other.
Survivor Man - S4-E7
Continuity mistake: In "The Alliance" (1-4), Pam says that the next office birthday is Meredith's, but it isn't until the next month. Later, in "Survivor Man", it is said that Meredith's birthday is at the end of 'Birthday Month', when many employees have birthdays close together. It wouldn't be possible for Meredith's birthday to both be the next office birthday but also at the end of the following month, which is stated to have many other birthdays in it.
Continuity mistake: When the Dunder Mifflin lawyer says "she thought it had to do with her recent breast enhancement surgery," the woman on the right side of the screen has her hand on her forehead. Then the shot changes angles and the woman's hand is now resting on her chin. (00:08:45)
Branch Wars - S4-E6
Continuity mistake: Earlier in the show we see Michael trying to get Jim to go on a "sale" to crush Utica by pumping him up in the conference room and when he turns to leave he sees Toby in an orange bow tie for The Meeting of the Finer Things Club but later in the episode we see Toby wearing a greenish/brown tie. (00:07:00 - 00:11:00)
Launch Party - S4-E3
Continuity mistake: The way the numbers on the sales board are written by Andy change in between shots. (For example, the "305" is written differently, but still "305"; not that it becomes a "380" when Andy changes the number).
Suggested correction: Michael didn't establish the contract with Hammer-mill. Rather, he locked them up as an exclusive supplier. It's unknown if they were already selling the products to Dunder Mifflin alongside Staples and Office Max.
Wrong, Josh says they cannot sell Hammer-mill products as they are exclusive to Staples so therefore they wouldn't have been able to sell there products alongside as mentioned before until Michael made them an exclusive to them solely, Dunder Mifflin. Therefore the original mistake stands true.