Hello alexg, I could find another postal bayonet by the same maker and with a number close to the one shown here and it has EXACTLY the same font as the one shown by you so for me it is without any further doubt an original one.
I do understand your thoughts concerning your wallet. If you are happy with the bayonet you are free to buy it. As said, in case of reselling it (also a point of view concerning your wallet) you will have a hard time.
In earlier days I also did buy items in not so good condition but finally I never became really happy with them.
These are only MY personal thoughts, regards,

DRP.JPG (13.07 KB, 106 downloads)
wotan, gd.c-b#105

"Never look for sqare eggs" as a late owner of an original FHH-dagger used to say.