I wouldn't really expect there to have been all that many skims, unless you know for sure otherwise. It isn't done automatically with a rebore; it's not usually necessary, especially with an iron head.
I'd be inclined to measure the head & barrel thicknesses if you want to be sure. The unskimmed standard barrel is 4" from base flange to deck.
Are you experiencing detonation? If not, dont worry. 7.5:1 is super low, even if it has had .040" off and its now 8.5:1, that really isn't going to cause any concern.
You may be trying to fix something that isn't broken.