Rory and Dean discuss their old anniversary date as the 24th. They got together the day after her birthday in Season 1; in that episode, Rory's birthday invitation lists her birthday as October 8th, making the old anniversary the 9th.
When Rory and Lorelai are taste-testing the cakes, the shots flip between a shot from behind the counter of Rory eating the raspberry cake and a shot from behind Rory where the cake is untouched.
When Max is eating breakfast with the girls at Luke's for the first time, the coffee cups change from red to blue and back to red.
Miss Patty says to Kirk " The camera is still on the lens".
During the beginning of the scene where Taylor Doose is introducing the new crosswalk/light, when the camera moves from him to Sookie and Lorelai (and after Lorelai asks Babette if she is coming to the bachelorette party), you can see a sound man crouching in the background, complete with Sony headgear.
At the drag club, Emily marvels that it was 34 years ago that she married Richard. But in Season 5 (in "Wedding Bell Blues") Richard and Emily reaffirm their wedding vows on their 40th anniversary. That means at this point, Emily and Richard were married 37 years ago not 34.