This *shouldn't* happen, as each is a separately registered event. But who knows, maybe the events are submitted together? (I don't think it's possible).
It does happen this way. When DD runs these two days events, the results are submitted together. The PDGA knows that they are separate days, but only split them into two if there is a huge discrepancy in the scores versus the ratings (rain one day but dry the other).
Sometimes, that doesn't even happen as it should. Last year's Frostbreaker was a great example, where it snowed an extra 3+ inches on the Pro/Adv day. Somehow, the PDGA didn't see a big enough ratings gap and smushed them together anyways. The ratings for the second day dropped probably 20 points per player.
EDIT: This is what I know from talking to Scott, unless I've misunderstood how he explained it to me (possible). Not revealing trade secrets here, just relaying the information I was given.