""System 1972:"
A second 5-6 digit serial system was introduced in 1972, overlapped onto some early 1973 models with NO rhyme or reason, and died a quick death before 1973 was out. This system never exeeded 6 digits, and the reason for its introduction remains a mystery. Regardless, it is here, and it will stay.

This system INCLUDES the Grand Prix and Super Course, despite the seven-digit serials (as mentioned in the next system, below) running concurrently on these models."

Forgive me, it's possibly 72 as well.

That's directly from Kurt's site btw http://www.kurtkaminer.com/TH_raleigh_serials.html