If an original bbl was used, see then if was given a 180 & refitted to place the spline cut under the wood if not machined off, filled, etc.
A second extractor cut at the 9 oclock position will tell.

It does make a nice looking profile whoever made the bbl & the blueing color is spectacular.
Question..is the proof mark an etching instead of a stamped mark?

Maybe they're all that way. I don't recall now what the mark looks like on my one and only Sedgley.