We decided to go with the Class letters as they are clearly physically signed with these letters on the boundary of the CAZs, and allows us to reuse the pass for multiple locations across the country. There are too many passes and it would be nice to have less. The many Mersey passes are toll passes that do not influence routing, the CAZ passes do affect routing. It would be great to have a visual difference between the 2 but there isn't.

Waze is not responsible for drivers not spotting the large boundary signage and getting fined if they do not pay any charges involved.

If you want to suggest to HQ that the pass should have more detail you will have to use the official Waze suggestion tool UserVoice. The app does show you the correct image in the CAZ popup if you don't have the pass and by tapping "add pass" the correct one will be added for you.  

I can't see the exemption passes in the app.
There's a CAZ Class C Exempt and a CAZ class D Exempt which are the only ones without a place name but no explanations of what they cover.
 

Unfortunately there's no explanation of what a Class C or Class D Exemption is. Neither the Birmingham CAZ website or the Bath CAZ website mention the zone class. The Vehicle checker only give a yes/no with no details of the classification of each zone.

i don't think many Waze users will know about the zone classifications (i didn't) and the need to research goverment policy to find out what passes to add shouldn't be neccessary. Considering adding an incorrect pass could lead to heavy fines I think it needs to be obvious what passes apply where.

As an app user I would expect to see Birmingham CAZ & Bath CAZ listed seperately alongside the other named location passes. There clearly isn't any worry about having too many passes, there's 5 passes alone for the Mersey tunnel, and the list is searchable.

If the app had the ability to show a pop-up info panel for each pass, detailing the cities, vehicles & times, then grouping the passes will work but without that functionality I think it will lead to confusion.
 
 

The CAZ class exemption passes have been used as when more CAZs are added around the country the same class system will also be used. Using the class-based system will save us having separate passes for each CAZ as they are created.

More info on CAZs and their classes can be found on the Gov.uk website at https://www.gov.uk/guidance/driving-in-a-clean-air-zone.