Mark,,
Its a good question - one I've often wondered myself. There are copies of magazine tests of the 250 MX1 in July, Nov & Dec 74 issues (Motorcyclist, Cycle World & Cycle Guide respectively).
The problem is, I think that it was sometimes designated a 75 model, & it was stamped w a 75 Vin # (5863), like the GP (5860) & MX2 (5864). The 1st # in the early canam system GENERALLY indicated year, but there were exceptions. Some websites list it as a 75 model, but the best one (vft.org/CanAm/vftCanAmNumbers.html) lists it as one of the exceptions.
It seems to me that its in the same unfortunate position as the YZB - available & racing in 74, but sometimes designated a 75 model (as the YZ was in the US) & so excluded. But now I've probably re-opened another can of worms!
Seems to me tho that the MX1 was clearly pre75 technology. And hasn't Boagy raced an MX1 in pre75? Or was it a TNT?