Styrenated resins are polyesters (auto shop fiberglass) and vinyl ester resins like Glasair's are built from.

Styrene is a reactive diluent so if you did lose some to evaporation your resin may be thicker and not want to wet out the fiber.

Epoxy should not suffer from this as nothing evaporates and they are reactive chemistries instead of catalyzing reactions.

The esters can solidify over time as they have inhibitors to prevent the monomers from cross linking. These are the resins with a few drops of catalysts like MEKP that destroy the inhibitors and allow cross linking.

A test lay up is always prudent. What to test depends on the end use of the part.

Regards,

Charlie Johnson