I'll leave the response as to the VIN numbers when these changed to either ChrisR or Mr Swan. I owned an engine in the late 3 digit era and the pipes were webbed with smooth ferrules so I believe somewhere under engine 900 for the smooth pipe. I've seen photographs of bike with 1 of each with the smooth clamp. VIN 248 with engine 342 has smooth pipes.
There are in fact several other variations to the crimping, in that the length of the crimp has changed over the years. Early bikes without smooth crimps (those with ribbed crimps) had less pronounced ribbed, but wider, wider crimps if you get my drift.
One interesting anomaly which I've noticed is the various differences to the engine fittings of pipes mainly the webbed with smooth crimps (the alloy part post crimp that attaches to the engine) This could just be casting variation although some of these castings have what I would describe as noticeable differences. I might see if I can compare what lines I have and post pictures in the future
