I just got back to lurking on this forum after having been away a couple of years and happened to run across this thread.
I have a 1987 31-2 (#48) and on mine the core does extend underneath the toe rails. In fact, I believe it is why my decks showed moisture on a moisture meter. The moisture ran all along the decks from the toe rail inboard about a foot(?) or so. I actually (over 2 or 3 years) drilled out/epoxied all the deck/hull bolts underneath the toe rail. Oh what fun