Yes, l an right, their was a big bum fight over it, yz 400 A, it looked the same as the yz or mx models 400 c, B, But the A was manufactured in 1974. And it is the only model eligilible.
No Dave. You're confusing two stories:
Story 1. Jody Someone got the YZ250B and YZ360B allowed in pre-75 racing. This was successful because there's Yamaha-published literature dated 1973, and the bikes were being raced in Australia in early-mid 1974 (ie: Before
any 75 models were released). I believe that Australia is the only country in the world to recognise the YZ-Bs as pre-75 legal.
Story 2. Someone else tried to claim that they had a 1974 model
MX400A, and that it should be pre-75 legal.
This fell flat on its face because there's no evidence of such a bike existing. At best, the hopeful person probably owned a pre-production or an early production MX400B that was made in 1974 - but it doesn't matter because MX400s are designated 1975 models.
To recap:
Pre-75 legal bikes: YZ250A, YZ360A, YZ250B, YZ360B.
Not pre-75 legal bikes: YZ250C, YZ400C, MX250B, MX400B.
Bikes that don't exist: MX400A, YZ400A.