OT: Argentine 1909 bayonet question

I won a SUPERB Argentine 1909 bayonet (matching scabbard) on eBay to go with my lovely M1909 rifle. The set was covered in grease from head to toe.

I cleaned that off, and there were the darkened spots on the blade from grease staining as often seen on bright bayonets. Those polished out easy with Brasso brass cleaner and a soft towel. BUT, at the very beginiing of the blade, forward of the ricasso where the fuller starts, the discolour was heavier. I rubbed this with the polish, and 95% came away, leaving concentric rings - BOTH sides.

I looked at it carefully, and in fact these rings are ever so lightly etched into the blade. I was wondering, this is either a little pitting where the storage grease kept some humidity trapped under, over time lightly etching, or the Argentines spot-annealed the blade at this juncture to strengthen them - anyone know?

An anneal at that point would be beneficial (being the point at which the fuller starts so is a weak point), but trapped water also makes sense - but odd it is the same on both sides - it did look like heat blackening before I polished.

I checked his other 1909 bayonet he had online still, and it too has the same discolour "temper" at this juncture.

Opinions appreciated

I have an unissued 1935 Brazilian mauser. It came with factory target and matching bayonet. When I pulled the bayonet from the scabbard, the grease that was in 3 blobs on each side was hardened. It popped off liked dried clay and left a circle of pitting under the edge of where the grease had been. The bayonet looked like it hadn't been out of that scabbard in 70 years. The original shipping cases were covered with tin and sealed. Don't know how long ago the crate was opened. JL