You just can't tell with Lugers. And there's no way you can get the proper feedback you need from written descriptions. You need someone who KNOWS these guns to look at it.
( There are so many shysters out selling them as authentic, when they aren't, that its risky -- unless you're buying it as a shooter. And even that could be risky, IF it truly is a pristine as you say...)
The mags were generally serial-numbered, I think, and not stamped with a model number. (All of the authentic ones I've had showed a serial number that should match the SN on the frame.) The Waffenampt {acceptance marks} you mention sound authentic.
I recently sold a very similar Luger for $1100 -- [less dealer's commission]. I have a very nice shooter that I'd sell for $450.
An aside: I don't believe there were enough officers in the German Army to account for all of the "captured from an officer" Lugers floating around. Not to mention the "nickel plated, captured from and officer" models, either. (According to the experts, the Germans NEVER issued nickel-plated guns; all such guns have been "tweaked" by subsequent owners.)
Your absolute best bet is to take it to a gun shop that specializes in collectibles. (I used Cherry's in Greensboro, NC --
http://www.cherrys.com ).
Or you can offer the seller $600 and tell him its probably worth more...