Assuming you also scoured all the underneath flats for a makers stamp.
Not being a jerk wad with this next comment. Just stating a fact from my own personal experience. Though it may in fact be an actual Bill Large barrel…..if it doesn’t carry his stamp, there is no real way of verifying that. And unfortunately as a result, it’s just an “unknown” and unmarked barrel.
It could have been a 42 inch Large barrel that was cut down on the breach end and and re-tapped for a breach plug, thus removing the makers mark. A little Unusual to do it that way, but a possibility. But if so, they also removed the proof. (Rifling patterns alone won’t do it). At least when the time arrives for reselling it. Hard to claim it’s a Large, without a way to verify it’s a Large. Sort of like having a Hudson Bay blanket without the HB label. It’s just an unmarked wool blanket at the point it’s sold. My 2 cents FWIW.