On steered axle, every locked wheel gives a 25% allowance, this count for every steered axle. (And only steered axle)
The DTP no for trucks are computer generated and actually have no meaning on their own.
The DTP no for trailers there is a formula for Digits 2,3, and 4, but cannot find them neither in my memory or in my computer.
The first digit is the amount of axles
The 6th digit shows ABS / EBS or nothing and what type.
The 5th digit is the important one: 3 means parking on axle 1&2
5 means parking on axle 1 & 3
6 means parking on axles 2 & 3
7 means parking on all 3 axles
It’s similar to 2 axles with 3 being both axles.
For PSV, there is a DTP no, but doesn’t get used, instead they use a simplified brake code, the first 3 digits are vehicle weight, the 4th digit is the amount of axles, the fifth split or progressive secondary, the 6th what axle the parking is on.
That is as far as I can remember, must have a better description somewhere, will have a look for it and update.