After clearing everything off the decks because of an afternoon thunderstorm, I thought perhaps I should try and hone in on the known bad spots. So, just forward of the section I just did, I made another cut lengthwise to try and just get the area around the chainplates.
Bingo. It was nice to see some bad core. (Did I just say that?) In any event, it was way easier to remove the material for these "sub" sections.
I'm already planning on replacing my chain plates, and looking at these soggy gaping holes in the side deck has me thinking about external chain plates again. Besides three less holes in each side deck, I think they look pretty shippy too. I'll have to hit the "search" button.