Lot's of shows can be inconsistant from time to time with storylines. I think Dorothy's prom was the biggest one ever on this show.

In one episode, it was stated that Dorothy and Stan went to the prom together (and Stan forgot to buy condoms).

In another episode, it was stated that Dorothy went to the prom with her brother Phil (and she was the only one from her friends on the tennis team to show up in her tennis skirt)

In another episode, it was stated that she didn't even go. John Naretti was going to take her but Sophia told him to get lost.

Were there any others?