I don't beleive that a matching magazine adds $925 to a gun. At least not that I've seen allowed me to sell it for that much more
Blue Book is a guide, but I have found them to be either high or low on lugers; more accurate is what the market is showing, i.e. gunbroker, Simpson's, FGS, Joe Salter; (when it sells and then deduct about 35% for retial versus collector to collector)...