I believe we are "officially" (?) covering LotR with all of our prior knowledge of both how this book ends and all the background material, but making an effort to *also* try to observe the work as a first-time reader with none of those at our disposal. Because we all know the material so well it is often a struggle to enter the first-time reader frame, but it is a rewarding struggle. It would, however, be a disservice to the project to restrict ourselves to *only* the first time reader perspective, or *only* the loremaster perspective. It's not likely we could afford the time to do this twice, so we have to try to do both in this one pass through the book.
There are also some questions that can definitively be answered by the background texts, and others that can only be suggested. For instance, last week when we were wondering if it was necessary for Sauron to have dominated Saruman (via palantir) in order for him to have fallen, we can see that in previous revisions Saruman was already falling even before the palantiri were invented in the author's mind. So it is possible for him to have fallen on his own. That's the sort of thing that the background material is excellent at sniffing out. The endless ret-conning of how early people suspected Saruman is the other side of that; because it contradicts what is in the published book, it can't really be taken as a finished product to add to our "fact" supply.