Thanks, David... I just received Dr. Jim's book a couple of days ago (fantastic, by the way) and have read the Brophy and Houchins chapters, as well (along with all of the Double Gun Journal articles and threads here on the topic). I know I've read that the early 3" guns weren't identified as LR until sometime in 1925, but I guess the question (that I know has been asked before here) is "What's the difference between a gun that was ordered with 3" chambers and a reinforced barrel lug/forend loop and a "LR" gun? Could you really order those options but specifically say "...but I don't want it to be LR"? I'm pretty sure the notion that the frames, chokes, or weights were different has been proven untrue.
I realize that the LR designation in the ledger is what determines the production stats, but the ledger code of "3" that I referred to in my gun's letter is what is really driving my questioning. Maybe Dr. Jim could comment on whether what he saw for my gun is unusual for pre-1925 3" guns or not. And also, what is the earliest serial number/date for the LR code to appear in the ledger? In other words, when my gun was finished in February, 1924, were other guns already tagged as LR and for some reason the person that ordered this one chose otherwise? Just in case it matters, we're talking about serial number RE6978x.