Sounds like osmosis. You really should determine if that is the case.I
believe there will be water in the blisters if so.

The liquid in most blisters isn't water.
When water penetrates the gel coat, (as it will do because gel coat is normally
porous), it reacts with any little microbits of dirt or etc that got settled on
the mold after the gelcoat was sprayed but before the skin out mat was laid in.
The chemical reaction forms a sort of solvent- particularly with a polyester
(vs vinlyester) layup. Next time you're popping a hull blister, hold some of
the contents up to your nose. Most typically, it will have a chemical
smell...almost reminiscent of Acetone.