My boat had a lot of those tiny blisters that came and went with wetting.
Almost a calico pattern. They were just very shallow surface blisters, and mostly disappeared as I sanded. (I sanded the bottom down to bare fiberglass and put on a new barrier coat, after drying out in 100° weather in semi-arid climate.). There were maybe a dozen serious blisters that required actual repair, which was easy.
I actually hauled the boat in February and there was a hard freeze immediately afterward. Most of the "real" blisters burst on their own. Also the there was some freeze damage to the rudder, which was full of water. Still dealing with the deck, bit by bit.
All this is par for the course for an old boat. Not a big deal if you're a DIY guy. Probably expensive if you pay someone else to deal with it. But I doubt that there are (m)any affordable older boats that don't have these problems.
I was looking at a couple of Valiant 40's as the possible "next boat." Now those have
serious blister problems! Makes any problems with Ericsons look trivial.