I have been doing more research on this; here is what I have learned about blister repairs in addition to my previous posts...
While attending the StrictlySail boat show and conference I was listening to the owner of MAS epoxies discuss various hull and deck repair techniques and here are some things I got out of his discussion:
The hull must be dried out to a moisture reading of 0.05% before applying barrier coats over either the existing gelcoat or stripped gelcoat. You can do this by letting dry for several months and checking periodically with a probe type moisture meter (the RF type can be incorrect by up to 50%). You can speed this process by tenting the lower hull and using space heaters (like the oil-radiator type) to get the temp up and promote evaporation.
The old blisters should be opened up ground/feathered out to good fiberglass and the hull should be stripped down to the gelcoat before allowing it to sit and dry out. If the blistering is severe (where it would be time prohibitave to grind out each blister); you should have a prof. company come and strip the gelcoat completely off. If you go this route dont bother stripping paint let the prof. company do everythig to remove the paint/gelcoat.
Fair out the bottom; using epoxy mixed with colloidal silica and strand silica to peanut butter conscistency; and/or a commercial epoxy base fairing compound. Sand flat, wash clean and after the hull has dried to .05% apply your barrier coats.
Here is where it gets interesting. You can either use an epoxy base paint or use 100% epoxy resin
If you use the resin be sure and use slow-set hardener. Have a friend rolling it on and then lay it off smooth with a bristle brush. MAS recommends a min of 5 coats of epoxy (follow mfr's directions regarding re-coat times). If you stripped the gelcoat, a layer of fiberglass matting should be applied to build the surface back to even with the hull above the waterline. Be sure there is no resin blushing (an oily residue) on the surface after each coat; if there is you will need to scuff sand and wash between coats. Since epoxy resin is not a paint; it will be more impervious to moisture than a paint based barrier coat and the gelcoat. Once this is complete you can scuff sand and apply your anti-fouling paint.
So in the case of Frank Langer I'd say that if the boat was barrier coated with epoxy; it was probably done properly (ask who did the work and ask what the procedure was). If it was stripped not allowed to dry out and barrier coated with epoxy paint and it's possible that you would be doing this job again sometime soon.