I guess the slide is the main question.... does it have any "collector" value since the SN area is milled. I've just never seen a Sig with that area milled. I think the milling was done by the factory, too nice of a job to be by an importer and there are no import marks on the gun. I do like the folded steel slides because they are a bit lighter than the milled versions and has an indestructible internal extractor, I broke 3 external extractors on a P226 TacOps I once had. It left a bad taste in my mouth with Sig and their MIM parts so I swore off "new Sigs till this gun popped up. (I needed another service size pistol like I need another hole in my head)lol.
Most Police and military trade in guns show crazy hard wear on the exterior which is why it's hard for me to believe it's an ex service gun or parts kit gun.
(BTW, the SN is on both sides of the frame)