Your slide was most likely refinished at some point that's why your markings on it are blued. For some reason, some pistols had that stamp ground off. That mark is the equivalent of a WWII Waffenamt. Mine now has a nice patina and I wouldn't trade it for anything. In case you can't tell, I'm a HUGE HK fan (classic, innovative HK, not the new crap). Those who know it to be the finest pistol ever produced 2.
Sierra Generations Family Tree Download Charts on this page. I always say: When talking about the P7 that there are two classes of people 1. It is simply THE BEST pistol I've ever owned.