If any group of guns would be different, it would be the M-17's off of the military line. I'm not sure how Sig would tweak the conventional P320 design to change grades of gun. As best I can tell the P320 was designed from the ground up to be economical to produce. The firing control group doesn't seem to have many parts that could be MIM and is a lot of stainless steel. MIM bothers me a lot less when the overall design was created from the ground up to support MIM parts. This is why H&K was successful with MIM but legacy Sigs had problems. The only possibility that makes sense is that IOP guns would have upgraded part assemblies implemented first. For instance, the ejector system has been completely revamped after initial problems. I'd be that those new parts were used in the IOP guns before the mass produced guns. Once Sig exhausted all of the old parts on the commercial line then they would have rolled in the new stuff.