Man... I've had two Lugers: one a shooter, and another that was a collectible. Never again.
There are just too manya variations, too many fakes, and too many charlatans running around.
If there's a gunshop that deals with collectibles anywhere in your area, let them look at it, and tell you about it.
The gun could be worth $500 or $5000, and you just can only get a general idea from the Blue Book.
(When I sold the collectible, recently, I had two different people, both of whom were knowledgeable and expert, look at it. One felt parts of it had been faked/restored, the other felt that it had been "touched" up a bit, but was basically a sound gun. He bought it for resale, and it eventually sold -- with holster -- for about $1200. Had it arguably been MORE authentic, it would have been worth an extra $500 or so. To the best of my knowledge -- it was a "bring back" from a neighbor's uncle from WWII -- it hadn't been futzed with, but he probably did touch up the backstrap with cold bluing.)
Any "adjustments" to a true collectible greatly reduces its value. Even rust is more desirable than adjustments for some collectibles.