John is right, 501 first made its debut in 1983, so I'm 1-2 years out at least.
In my defence, I knew that range of frame numbers went from 76 to 84, and was guessing at 81 +/-1 based on how high the number was, but not a bad guess, eh?
Edit - earliest reference to the criterium I can find is 1987, and that year they were fluorescent pink. The Falcon era Criteiums were 531.
Edit #2 - just to confuse matters, Claud Butler also sold a model badged as Criterium in the 80's. Identical frame design but in 531, but with different forks. The OP may not know but that that time Holdsworth and Claud Butler were made by the same folk, with the sportier bikes tending to be badged as Holdsworth and the more touring oriented models as CB, but that wasn't a hard and fast rule.