That's correct Sum,
On the car side there was never a designator other then stating "Snell rated" early on, then later(somewhere around 2003 I believe?), the "M" (or) "SA" designators were added to the rulebook in the car section (and became under question by a few).
With the bike side on the other hand, there was no "M"(only) designator until 2007(still under question? yes).
At that time(around 2003 or 2004 actually I think?), the questioning pushed some of us to look deeper into reasons that we wouldn't (or couldn't, other then the written rule) allow them to be swapped in vehicle type. Seeing as we were bike guys(and a girl
) studying it.. we didn't see where it effected our MC rules and the car guys are running the place sooo on to the next gig. Then, again in 2006 we looked at it deeper when it was being discussed about the "M only" designator for the bikes (allowing SA helemt's on bikes wasn't anything that made it in the rulebook as you can see, but it's not something I'm going to shoot someone down for in tech either). We do let the car guys that talk about hearing a bike helmet for reduced weight, visibility, etc... that the fire rating is not there and it's not a good idea from what we studyied in the past.
At anyrate, you and Larry are both correct in the reading of the current rules (but like some other unmentioned rules), that doens't make them right... just improperly (imo) transposed over the years.
Todd
EDIT - PS: the above references are ECTA related (sorry, it's all I know fairly well right now), and I haven't had time (YET) or have all the SCTA rulebooks in my posession currently to see the progression of the original rulers.