Bloomin' Volexes that I've been using are even more confusing. There is
no numbering on the MCBs, but the (already split) neutral is numbered
(IIRC) 1 to 8 (L to R) non-RCD, and 8 to 1 (L to R) on the RCD side

I don't get these issues. RCBOs rule! Easier to wire up, too, as the entire
cable goes into the top of them, without touching the neutral bus bar at all
(which is not split), so no need to work out how much longer the neutral
needs to be than the live and leads to neater internal wiring.

Christian.