[rob love]

That is the later version of the DND numbering system. Actually, it seems to be a mix of the later and the earlier version.

Early numbers would be the Z over a number format such as 41-1-234. The 41 would be the year the number was given to the vehicle,they all have a one after that, and the 234 would have been a sequential number assigned. I owned a 1940 once, and it had a 41 in it's prefix. A check with the war diaries of the unit it belonged to showed several other DND numbers in the same range applied to other vehicles in the unit, from staff cars to tractors.

Later they went to the numbering system like you have shown: usually two digits followed by three digits. I have not seen a rationale as to this numbering format.

To find some unit history on the truck you would need to find other markings on the vehicle. Often, over top of the Z would have been another unit marking, such as A4RCATC. That would be the unit. Later, they went to the coloured markings with numbers in them...these were usually on the front cowl and the tailgate.