When we discussed Romans 5:12 the context I gave you were three preceding chapters and the fact that "all" is transformed into "many" a few verses down. It would be entirely proper to explain scripture with tradition -- that is the the only way, generally speaking, -- but in conversations with Protestants I do not do that, and I did not do so in this case.
I appreciate that, thank you. I think your arguments are stronger to a Protestant for doing so. And, I absolutely acknowledge your right to explain scripture within tradition according to your beliefs. That's cool with me too. :)
As to the difference between "all" and "many" (v. 15, 19), One explanation that I think makes sense is that concerning Adam, "many" is a distinction to refer to all of his progeny (all mankind) but not to himself. In contrast, the "all" in v. 12 (and 3:23) refers to all who have ever lived except Jesus, but including Adam. The alternative is to say that only some bear the sin of Adam as opposed to others. That doesn't make sense to me.
On the flip-side, Paul tells us it is not the same. Here, I think the use of "many" refers to the elect, since we all know that not everyone is saved.