this is assuming no one has added pure acid it the electrolyte in an effort to squeeze more life out of them, but i would find that very unlikely.

yes if you have deminished capacity it is because the plate are worn thin, at the point.

you might just run them through a few cycles and keep fully charging them, to see if they might recover a bit more.

getting the specific gravity back up with a good charge leads me to believe you have some batteries that have some useful life left in them.

keep a log book on them and put em to work.