Not sure whether I understood you correctly.

You can only create WDM devices for physical existing ports.
Analog 1-8, ADAT 1-16, etc

So the maximum number of WDM devices is the number of physical ports, that an interface has.
You have as many I/O ports as you have, not more, not less.
Therefore it makes no sense to document the number of WDM devices for each device.

Maybe you should think a little more about the following point, why we have to create WDM devices under Windows:

I think we all agree, that for applications that support ASIO (like DAW) you only have to load the RME ASIO driver to be able access the I/O ports. Ok ?

But for Windows and Applications, that do not support ASIO, you need to create Windows compatible WDM devices.

By creating WDM devices you only create Windows compatible drivers as needed, but you do not get more physical I/O ports by that. You access the same physical ports on your recording interface, only through a Windows compatible driver.

In a perfect world Windows and Windows Applications would all have ASIO support compiled in. Then nobody would need WDM drivers anymore ...

Got it ?