OK so it may be a theatre mod, that could be making a story to fit but it would seem unlikely (IMO) that you would take that much material from a blade merely "cleaning it up" and if it was damage removal it must have been a hell of nick!! So the other side of the coin is that it was damage and it took a few tries at getting the balance right.

I've got the knife in front of me as I write this and on close inspection the blade doesn't seem to have any major surface corrosion and the stamp is pretty crisp so I'd go with damage correction or deliberate modification.

On another train of thought how much material would frequent (possibly over zealous) sharpening remove? I know I've seen old pocket knives with blades that are hardly still there reasonably often. This may tie in with the original stone being replaced, I heard the ones around this era were a bit soft too.

The original owner was Gunnery Sergeant Leonard H Smith 614489/6713 1st Marine Aircraft Wing. How would I go about seeing if he was still contactable today? Tall order I'm sure but may be worth the effort.