The 64 in the door number has no relation to the year. That style of numbering replaced the earlier style of (ie
41-1-1083. In the case of that style of number, the 41 reflects the year the number was assigned to the truck (usually also the year of manufacture, but not always.)
From what I have seen in war diaries, the earlier door numbers seem to have been assigned in batches in relation to the units that held the vehicles, regardless of the vehicle type. A station wagon could have the next sequential number to a run of F15s, and an artillery tractor could be the next sequentially.
The latest CMP I have heard of was the KL welding lorry with the Camp Borden CE section. If I recall correctly it was in service until 1974. Even later, however, was a CMP 2 wheel compressor trailer hiding in the compound in Flin Flon Manitoba. We would still do annual inspections on it until it was released from service in 1987. I am now the present owner of that one.