after reading this i think i am gonna play it again i forgot many things now because of the longer updatesSo... You don't remember the night of the big pool/pizza/best butt contest party? It ends with an edging exercise; set up by Jamie and Shauna, in which MC is with all the girls he's been with previously - including Rachel. Before that, I think it's the day before or earlier in the day of the big fight outside the bowling alley, Jamie does a checklist conversation with MC about several girls - including Rachel. During that conversation MC says he has had sex with Rachel "a few times".
Those are both pretty major event/conversations to forget about but, they do happen and have always been part of the story afaik.