For that particular model, I don't think ANY carlton website will be very helpful because I believe that one has stamped dropouts and the numerology for the stamped dropouts (there is no letter prefix on those) has never been explained.
Happily, it has to be a 1973-4 bike, and here is why I believe it :
(1) The "CARLTON" block lettered seat tube decal was introduced in 1973, at least in the USA it was.
(2) The reynolds tubing decal is definitely 1973 or earlier. I believe that these decals did not run out and get replaced by gold-banded-below "Reynolds Tube Co. Inc." decals until some time in 1974.
The bike cannot be 1972 or earlier, or the seat decal would be, "Carlton, man-on-a-bike".
The bike cannot be 1974 or later, or the 531 seat decal would say, "Gauranteed Built with Reynolds==531== Butted Tubes Forks & Stays" "Reynolds Tube Co. Inc. Birmingham England."
The "man on a bike" head tube logo was discontinued in 1977, replaced by a decal very-much like the seat tube decal (but not exactly like it.) So the head tube is pre-77.
Those lugs are something unusual, I haven't seen many Carlton Competitions (I've seen many Raleigh/Carlton Competitions), and most of them had nervex lugs, but the last time I saw lugs like that was on a 1978 carlton super course.
These bikes are really nice rides, in fact, I normally have the best time on club rides on my raleigh gran sport, which is an equivalent bike with raleigh badging.
- Don Gillies
San Diego, CA, USA