John,
I've not seen a 1920 or otherwise Weimar marked police luger without a hold open either.
This is one of those "simple" questions without an answer- we cannot know if a hold open was ever added to a frame without one after 1914. Why would one do it, when 1000's of frames with them were available? I would think it a fatal flaw, just like a crack would have been when selecting frames for re-work. AGAIN JMHO.
I regret ever offering an opinion on the OP's un-knowable question.
