I thought all production was switched from the USA to the far east in 1981? so any frame numbers without the letters should be pre 1982? I stand to be corrected though
you may be right there ratty, although in the crossover you could still get an American made frame in 1982 (this may only apply to the proline frames though) which didn't have the "R" in the serial. my prolineII from BITD (1982) had a consecutive number but may well have been a 1981 build as i ordered it late 1981.
i think mxII frames started production in japan from 1979, from the info i can find these frames had "RJ". i'm not 100% sure on this as i have yet to find info that confirms or denies this.
my black mxII frame has a consecutive number, so i'm led to believe it is an American frame, probably from 1979/80. my white frame is an "RC" series 3 which would tell me it's 1983 Japanese made. a friend of mine here in aus has a mxII with "RA", which to me would mean 1981 Japanese made.
there's also some slight differences in the "redline" stamp on the BB which may have resulted from different manufacturers. i only found out the other week that a mob in New Zealand were also an authorised frame builder for redline.
having said that, i don't really know or care much for anything after 1985 as that's the end of OS for me