Model 40 is the designation for the V8 passenger cars. There seems to be no apparent reason for the number choice.
Then a couple pages later it breaks them down a little more, to 40-720. This reference is from Windsor Ontario ( Canada ) published in 1938.
This is from a different book, but has pictures, should have started here. I read it for the articles.
Internal reference number for parts and service. After 32 a lot of stuff was unique to the model year or series, this way it's easier to make sure you're using or ordering model specific parts. Yes, it's that mundane of a reason.
Trying to apply logic to factory numbering systems will usually make your brain hurt. For example, 1954 Olds cylinder heads have a 7 cast on them. 1955 heads have an 8 cast on them. 1956 heads have.....a 10. What happened to 9?
For some, a chassis designation is used for parts. A prefix in a part number cam be the chassis designation. A German manufacturer uses the prefix 000 to designate a part that fits multiple chassis. Bulbs, fluids, clips…… It simplifies parts ID. Pick up a part, read the prefix and you know what it fits
Because “Ford” didn’t realize that in 1940 the cars they built that year were going to be called 40 Ford’s!
Then there was this from the "I bet you didn't know this file", and it is just one example of some of the Ford wackiness that came from across the pond. So much more Here: https://www.fordyandcmodelregister.co.uk/model-identification.html
There are a whole lot of things in this world that don’t seem to make any sense except to the person who created them. Some ID numbering systems are intuitive but others seem like they are in some secret code for some unknown reason.
When I was a kid, grandpa called his 1937 Ford a 60. It was years before I learned that his car had a 60 HP engine