it wasnt so much that there was a lack of reaserch on the flat slide issue, there was and through this forum considerable information was supplied, considered and discussed.
The reason why it was decided to cut off the eligibility at pre 78 was it was undeniable that flat slides were generally available in the pre 78 period. We were correcting the "you cant use flatslides - period" rule that technically prevented bikes fitted standard with them using them!
The problem with pre 75 is more about management, they were not readily available and they are / were rarely used pre 75 and although it can be argued that some were available like early Mk1 Lectron etc there had to be a decision made.
How do you determine what flat slide is OK or not? Are the riders calling for the inclusion of specific indervidual units to be included in the MOMs? Its up to the riders, put forward the case and your voice will be listened to.