A lot of Lugers in the US and for the US market had the stock lugs ground in the 1950s and early 1960s, people being scared of the BATF even then.
Any Germanmilitary Lugers I have seen have had the DATE stamped prominently on the receiver ring. Earliest I have had in my hands was a 1912 DWM which was interesting because it had no hold-open and had never been modded for one. Later, of course, they were built with the hold-open. If the date has been buffed, sometimes it can be raised with etching, although I am thinking a less-destructive method might do well, given the industrial X-ray and other imaging equipment available these days. We are getting usable results with UV light on compressed wood which has been sanded; surely there must be something of that ilk which would work on steel. Perhaps talk to an aircraft mechanic.
Sorry not to be more helpful.
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There are undated Lugers, of course, but any I have run into have been commercials... such as the 99%+ commercial Navy I ran into a few years ago. My bank account was only 4 figures short of being able to afford it!