Welcome to AAPK! Hope you enjoy it here.
In answer to your question:
Your vibe receptor is screwy (

) because you haven't looked at enough Robeson knives to know what their tang stamps looked like prior to WWII.
If you are one that thinks any tang stamp should look like a Case Cutlery Co. stamp or that it should look like Bernie Levine's published description of a genuine tang stamp; i.e. that there must be carbon left in the recesses of the stamp after the striking of a hot carbon steel blade, you're never going to find an old Robeson knife to your liking, because they all had stamps just like the subject EO knife above.
I have no idea how or what Robeson did to their tang stamps, but prior to WWII, the stamps were clean, shiney and did, indeed, have the appearance of having been etched. Were they? I doubt it it, but they do look it.
Go to
http://www.RobesonsRme.com and click on the "
HISTORY" icon. Scroll down until the tang stamp section appears and look at them. Those are all genuine Robeson stamps.
Look at the post - WWII stamps and you'll find the dark carbon deposits which you're thinking should be omni-present.
What changed? I have no idea.
A word of caution. The website will lock-up your computer unless you have a gig or more of random access memory. If you're running 512 megabytes, don't go there. It wasn't built by a computer guru, so it's a little picture heavy.
Charlie Noyes