Trouble with gelcoat

[Randy]

This looks like trouble here. Hope I can get some expert advice.
My intent was to remove bottom paint prep hull and re-apply barrier coat and an epoxy paint. I took off about 5 layers of bottom paint with a chemical stripper then began sanding. I uncovered what looks like tons of small blister. I'm unsure because they where filled with paint and had no moisture. Is there any other reason for this type damage to old gelcoat? Can I just fair the holes or does every one need sanding/ground down? Thanks for help.