Link won't open, for me anyway, not a forum I am familiar with... while I have been known to be wrong before (my wife tells me all the time I sound smarter than I really am, - and she ought to know...), I think I know the subject as well a someone can today.
Generally, rifles that pass through a depot receive acceptance, this is for accountability and the German military was all about accountability and responsibility in work conducted. They slapped acceptance (waffenamts and HZa stamps) on everything, even little meaningless components that had to stand alone in the ordnance system. Now were there instances where a depot overlooked an acceptance, or let one slip by, I am sure that occurred, - that said all work was suppose to have been marked and the vast majority was, especially at the larger facilities.
A far more likely scenario is that the marking was small or lightly struck and it was worn away, - this is common, often all you can see is a impression or indention. Sometimes a partial. The wrist is a common wear point and it probably doesn't take long to wear a small marking down. This is far less a problem in the Republican era, they used large stamps and early on placed them on the sides, often over the cypher (Cassel did this often).
