I think you're not quite following. That's all nonsense because you are STILL applying to it the logic of the North American practice, which doesn't work in this context
. First, de jure the A and B units here are both cab units, second, the booster units are C and D (А, Б and В, Г accordingly if you wanna mess with our cyrillics), that's how they're assigned, and they have some differences between them. For example, least I know, the C has a toliet and the D has some kind of quarters for crew - those aren't impacting the locomotive performance but still are technical differences.
So those are not identical sets, those are complimentary sets after all. And as I said already, in this practice
, no one looks at them this way anyway, as in, the pair of booster+cab unit, they are viewed as a single loco because they are designed and certified this way
. You probably could rearrange the sections some particular way, but this would be a deviation from how this loco was intended, and won't be a single loco in the way it was intended. And especially, since the electric loco is obligated to have at least two pantographs, you can't operate the set with less than two cab units, so all this AB+BA concept totally does not make any sense here.
>ABBAABBA since that would technically count for the same reason ABBA seems to count?
"ABBAABBA" is not only not complimentary, it won't meet the local criteria of a whole locomotive. At the very least it would lack the passage through the whole loco, which is already enough, then, I think, it would lack the HV bus connection throughout the entire locomotive. Atop of that, this series is designed to handle only 4 sections in multiple unit. Whether this is software or hardware, I dunno though.