By un-joined up thinking... I should have said I thought it was a 1981.

My twisted logic was pretty basic -
My Dawes, from 1979 ~ 1982'ish has the same crankset.
The Carlton factory closed in 1981
An NOS frame was quite likely to have been left over from the upheaval of closing the factory.
The price was really low and I figured low meant later.

I'll crawl back into my corner now and try not to be seen.