Matt,

I'm not sure I'm reading your question correctly.

I've never seen any reference to where there is more than A/B in RDs. Some of them have essentially what is AA/BB where the 'AA' may be something like Brushes/Busy Brushes and 'BB' Ride/Loud Ride. BIAB would cycle through the first set of AB and move to the second when the part markers repeated. For example, in a song structured AABA AABA the first AABA would be Brushes/Ride where the second would be Busy Brushes/Loud Ride.

Now if you're talking about multistyles, I've found that BIAB treats a C/D marker the same as A/B. Most of my customized styles have at least one multistyle where I have defined A/B with brushes and C/D with sticks. I even have some with E/F. In all cases, BIAB uses the related RD A/B instruction for those multistyles.

Did I read you correctly?

R