The ZDF etc. on the barrel is an importers mark and I quote from an earlier inquiry about this mark: "The markings are ZDF Import/Export Inc., otherwise known as Robinson Armament Company, P.O. Box 16776, Salt Lake City, Utah 84116. Their web site is
www.robarm.com ". The fact that your Luger does not have a frame cut could be because the modification was never completed, since the magazine safety was proving to be more trouble than it was worth. Or, there are some examples where this cut has been expertly welded up during rework and is difficult to see that it ever was there. The hole was probably too large to weld up and is covered up by the side plate anyway.