How can season 3 take place during the 秒 semester after season 2 when both have a 万圣节前夕 and 圣诞节 episode?

This is something that constantly puzzled me. For a while, I've gone through a theory that due to a spell gone horribly wrong, Sabrina and everyone else in her area were forced to go through the same 年 twice while still having knowledge of the 年 before the incident.