No worries. BRCA Rules are split into two - Construction Rules and Racing Rules. This is because a Construction Rule requires a two-thirds majority of those voting to change a rule, whereas Racing Rules (including classes raced) only require a simple majority of votes cast at an AGM/EGM.
Construction Rules say what is allowed, and what not; what the dimensions are and their limits. We included 21.5 as it provides some Clubs with an alternative way of getting people racing with GT12. This was mainly because low-cost speedos with 1S capability were hard to come by, and wiring up a receiver pack or booster was not easy.
With the advent of two great low-cost 1S speedos from Mardave and Schumacher, perhaps the need for the 21.5 class will disappear. In any event, it was not adopted for Nationals as there is no equivalence between the two, and if the 21.5 was given any mechanical timing from the motor, it was often faster than a 1S/13.5.
The default combination - that is, everyone runs it - for Nationals is 1S/13.5 HTH
