Believe it or not, not everyone working in the gun companies feel the need to keep up on every change made to the products, let alone the reasons for the changes. Major changes? Probably. Minor, ongoing revisions and subtle improvements? Not so much, it seems. Sometimes you might get lucky and be able to speak with an engineer, someone else involved in R&D, a program/product manager, etc who doesn't mind sharing some additional info with an armorer. Remember the original proprietary accessory rail on the P99's? How about the odd down-turned point on the grip frame above the web of the shooter's hand? Those things were eventually changed in the P99's to features requested by S&W in the frames they bought for their licensed models. (The rails to more easily conform to existing lights. The grip tang? Well, we were once told that S&W engineers wanted a smoother, less hooked grip tang to try and prevent shooter discomfort in the harder recoiling .40 models. Maybe so. Walther eventually adopted it, though.) All I heard about the change in the frame dimension in the area of the sear housing block at one point was that Walther felt it was an improvement. Okay ... The ambi slide stop assembly made sense (but required a different frame). I suppose someone thought the extended mag catch levers were a good idea (although I found the original ones easily used, myself). The 'ramp' inside the trigger guard, at the bottom (to presumably 'guide' the shooter's finger to proper placement against the trigger face, so it wouldn't be dragged along the bottom of the trigger guard)? Well, that went away, for whatever reason, when the trigger guard was revised. (At the request of some heavily gloved gov users on the international market, where Walther has a strong presence? Dunno. Wouldn't be surprised, though.) The newer sights and the clamping sleeve would seem to be an improvement. The thin side "ear" of the notch on the head of the rear sight base plunger could become damaged upon impact, allowing the rear sight base to move. There's been some other slight changes and improvements here & there, and I certainly don't pretend to have had the chance to learn of more than probably a few of them. I always wondered when/if Walther would design a way to incorporate the ejector into the sear housing without molding it in the housing. (The M&P pistol is an excellent example of how it could be done, although the M&P uses a steel housing block ... and they probably gained a fair amount of experience being the importers/warranty providers for Walthers, as well as selling/servicing the licensed SW99/990L's. ) Of course, when Walther designed the PPS they adopted a steel "housing" that not only incorporated the frame rails, but the ejector, as well. So, it wouldn't surprise if they'd found a way to incorporate some slight improvement in their frame at some point. I've only been exposed to maybe 60 examples of the 99 series over the years, most of which have been SW9940's (but some 9's in both SW99 & P99). Several have been used to fire several thousand rounds, and a couple (a 9 & a .40) have been used to fire more than 55K rounds (last time I asked the owner, which was more than a couple of years ago, and he's continued to shoot them a lot). I've only got a little over 12K rounds through mine (a compact 9, being the SW999c). I've had a couple damaged rear sights & plungers, a cracked slide end cap, a couple of mangled slide stop lever springs, a couple of weakened extractor springs (one each in a full-size SW999 and P99 9), a couple of broken ejectors (high round count guns, meaning many thousand on one gun and just over 50K on the other). The only cracked frame was that 9 with the case head blowout. I like the 99 series quite a bit, myself.