I'd like to add that T227's may be included on the list of cards that can be soaked.
I was the only bidder on this McDermott in a recent auction, and I bought it specifically to try as my first soak. The card looked terrible, so I figured I didn't have much to lose. The back was completely covered by thick, yellowed, heavy lined paper, and the text underneath was completely unreadable:
As per your suggestions, I used warm, soft tap water, a bowl, a pair of tweezers, and a q-tip. I gently slipped the card into the water and watched it sink.
After only a few minutes, the edges of the glued on paper began to curl up. After 15 minutes of soaking, I was able to easily lift most of the paper off the card. It would have all come up in one piece, if not for the white spot on the right center of the card. It was another kind of glue, or gum, or who knows what, but I had to pull with gentle-but-firm steady pressure for it to slowly let go.
After removing the paper, I replaced the dirty water and let the card soak for another 30 min. I wanted to ensure that any glue residue remaining would be gone before I placed the card on paper towels to dry.
I dried the card overnight using paper towels and a stack of books. I changed out the towels a few times before retiring, then checked on my progress today:
I'm thrilled with how it turned out. It's still a card in poor condition, but now at least it's one I can read and enjoy. For the $10 bid, it was well worth it.
Thanks so much to everyone for their suggestions!