As has already been said, the first Roadsters were just an 'S' with low pipes and different side panel decals. I think some of the new colours were also introduced around this time, but can't be certain (Fireflake Purple, Golden Bronze, Emerald Green etc.).
I have 13501X which the dispatch record shows left the factory as a green 'S' in May 1970. I'm assuming it's Fireflake Emerald Green (tank & panels long gone when I got hold of it), and not the plain 'British Racing Green' or whatever it's actually called as seen on early Fastbacks.
As I've found out, the dispatch records show quite a lot of overlap and out-of-sequence builds, with some 200 series bikes leaving the factory earlier than 135 series bikes.
Worth noting that the early Roadster pipes were tucked in at the head, similar to Production Racer pipes, and quite different to the later pipes which splay out more. Don't know if they are the same as the PR?
Norton Service Bulletin recommends broken 'S' pipes should be replaced with Roaster type, so it seems there were rather a few 'S' pipes failing in use and Norton just gave up on them.