Okay, first-
Put the knife down and unplug the router. Cut as little as possible. Save whatever you cut.
Presuming this is a polyester resin/polyurethane foam board, though I’ll add epoxy/styrene foam methods too.
For the big delams, maybe slice three sides, open it up and dry it out, don’t use a heat gun, that will make the delam spread… When it dries, fill (indeed overfill) with resin-filler mixture, catalysed light. You want to put in a lot so you get no air bubbles in there.
You don’'t want this getting hot as it goes off, see ‘delam spread’ earlier… Let the flap down and hold it in place with something, a weight or a strap or lots of tape, over wax paper. Let the excess filler come out around the edges.
Resist the urge to futz with it. You will only get air in under the old cloth, which is bad.
If it’s epoxy/styrene foam, open it up as above, but set it in a way that the water that got into the styrene foam, and it did, can drain by gravity. You won’t get it all, but be patient. Do the same with filler/resin mix but do up the epoxy exactly as the directions say. Replace the flap or cut-out piece as above and I would stash it someplace cool and dark until the resin/filler hardens.
Sand the excess filler flush with the deck. Lightly sand the area, clean it off dust free. Glass over the area, overlapping to undamaged un delammed area… Go thick as needed to bring it to a nice smooth surface if your original glass is a little low when it went back in., hotcoat, sand, gloss, sand and polish as needed.
This way, you don’t have to attempt a color match, a trick that never works. You don’t have (we hope) a your patch sitting there like a wart over the whole thing. You may see a little filler outline around the original glass, that’s acceptable.
As for where previous owner went muts with the boat resin botox treatment- look, by the time you go drilling and refilling and all that, I think you’ll only make it ugly. Unless you are really really good and really really lucky.
Sand the resin down flush that’s excess at the resin injection sites, lightly glass over, feather the edge of your patch and hotcoat/gloss as needed. It won’t be perfect but it won’t be worse and in this that’s about the best you will get
hope that’s of use
doc…