James, yes without doubt period reference is the best, just looking at the 2nd advert again helps me determine what I had always thought about this particular Dula and the markings on the rear,
The advert states these knives were
Das Gebrauchsmesser des Forst-beamten
"HFB"
Heer Forst beamten
I'd always thought the chequered grips on this piece were specially ordered at the time.
Thanks
Gary