I'm not sure where your "field number" values come from, but I can explain some precedence around the terms "device number", "extended device number", "transmission type", and "serial number".
The 16-bit device number was originally the only way to signify the uniqueness of an ANT+ device, but as the market grew larger, a need arose for a larger unique identifier, leading to...
The 8-bit transmission type field, which for ANT+ devices used to only be 0x05. As the upper nibble was not being used, manufacturers now append an additional 4-bit unique value to create an extended device number which looks like this:
Extended Device Number == Transmission Byte Upper Nibble || Device Number. A 20-bit value in total.
But some devices, like HR straps, tend to be used in large group settings, or for unique user identification, in which case a larger value than 20-bits is useful, hence the serial number. The manufacturer's information data page lists an additional 16-bits to make the device more unique, but requires listening to the device long enough to find the value, or forces the receiver to make a request for the data page. This results in this logic for the Serial Number:
Serial Number for Device == Serial Number from Data Page || Transmission Byte Upper Nibble || Device Number. A 36-bit value in total.
Hope that helps clear up any confusion.