PeterMark,
I have it on good authority that there were Comet numbers before C35. As we know, numbers are a matter for Simon; perhaps he will chime in here and say, just for the record, "I'm right" or "I'm wrong"? No more.
Peter
As per usual there is no simple answer.
Date wise in the works records C35 is the earliest production Comet with a "C" number but there was an ealier experimental engine but it did not have "C" prefix.
There were several series A's with an engine number lower than 35, mostly TT & TTR bikes and a few Comet Specials but date wise they are not earlier than C35. Basically the factory put one works record book with a range of numbers to one side for early TTR & TTC and those numbers drip fed out in no particular order.
Simon