Corrected entry: Clark and Alicia are in the basement of the school, as part of the plan to trick Alicia, and, as they go to leave, Alicia picks up her bag with Clark right next to her. A few minutes later we find out that Alicia has a kryptonite rock in her bag. She takes it out of her bag to get away from Clark. Clark felt no effects from the rock before that even though he was in such close proximity, and surely a bag would not be enough to protect his from feeling the effects.
Corrected entry: Earlier in the episode Lana is looking through Adam's journal which contains entries through at least the end of January. However, when Clark is taking Alicia home after their date, there are Christmas lights up due to filming during the holidays.
Correction: Some people don't take their decorations down right away. I have neighbors whom leave theirs up until February.
Correction: Being obsessed with him, she would also likely know that lead blocks the effects of the kryptonite. She could have kept it in a lead casing and would only have used it just in case. Otherwise she would have been hurting him for no reason.
Knever