One of them is probably here (in function ap_meets_conditions). Is there any
reason we cannot use r->request_time here?
I can't tell for sure right now, but the original concern was that dynamically generated pages that are forked into a cache (something done by RobH for IMDB) would have a modification time after the request time, and thus a later request for that same page (which has not changed in the interim) would be later than the IMS time and thus always result in a 200 instead of 304. I don't know if that was the same concern that motivated it here.
....Roy
