What is the model number suffix and how do I interpret it?
WD isn't likely to say...
"Model Number Suffix
The Model Number Suffix (characters to the right of the dash following the model number) is only for in-house use."
according to the available literature.
You apparently need to be a WD employee, with access to the local WD intranet, in order to access the documentation that decodes the suffixes. I'd doubt they'd publish the information here, if they don't want to make it available anywhere else.