Three things: 1) I am very sorry your dad was cheated, it is infuriating to see novice enthusiasts taken advantage of; 2) I would be astounded if the pawnbroker was as ignorant as you have been kind enough to allow. If he has been in business very long and attends gun shows his knowledge of Lugers would be far more than rudimentary...it is his business to know these things and the fact that he nicked your father for ~$1800 points to his lack of scruples; 3) You wondered at how quickly your Luger was identified and how it was possible to glean such detailed information from the photos you provided. You posed your question in a venue inhabited by Luger collectors and students of its history for a number of years...in my case 60 years...so you got instant research. Your ex-cop father can rest assured that the identification information provided is correct.
Best wishes and regards,