I almost lost myself in the crossfire.
Right, for sure, whoever whittled away the seat-stay lugs was definitely somebody who knew what they were doing....... (I think that is five dots) ....... (and another five) but, what is a bit special is going to that length and effort for all that 1 or 2 gram saving and then putting braze-ons for a rack mount......for presumably a touring bike. It makes little sense. It makes no sense in the real world.
My thinking is that the cut-outs are more of a signature of the frame build. Probably someone obsessed with lightweight frames, and your frame is one produced for a regular customer who wanted something lightweight for CX races. After a few seasonss racing CX, the frame being relegated to winter club rides then converted for touring, adding rack braze-ons to extend it's useful life. Then re-sprayed to what you see today. Just a guesstimate. There is no photo of the rear drop-outs to proove or dis-prove my theory / bullshit....are there specific mounts and/or drillings for racks, do they appear retro-fitted like an after-thought?
Eitherway, it's a little bijoux objet d'art because even in these parts, any road frame with a canti-hanger and canti-studs is a rarity.