A majority of the Class 15x subclasses do not align with the TOPS numbering. Class 158 being a notorious example where, for example, all of the Angel owned units are subclass /0 despite not being numbered as such.
Yes, and again, this is because the
Sprinter family classes (from 150/1 onwards) share the same
vehicle numbering system (such as the 52xxx and 57xxx numbers of the driving vehicles), which is why, with the
unit numbers, after the 150/1s being 1501xx and the 150/2s being 1502xx, the 155s are 1553xx (most of which were converted to 153s of course, hence 1533xx), the 156s are 1564xx and 1565xx (4xx into 5xx due to more than 99 units, so also doing the thing the 450s do, which go from 0xx into 1xx) and the 158/0s are 1587xx and 1588xx (again, also doing the "450 thing").