Actually the best way to identify the validator is by looking at the bottom of the unit. The harness that comes from the back plugs into the side of the CPU. If there are three plugs, (2 pin, 4 pin and 5 pin) it's either a WBA 10 or WBA 11. If there is a 20 pin plug and a 4 pin, it's a WBA 12 or WBA 13.
Even numbers (WBA 10 and WBA 12 ) are flash units (No plug in EPROM)
Odd Numbers (WBA 11 and WBA 13 ) have a plug in EPROM for programming
The head of the unit is interchangeable between all four models and can be misleading if you use the sticker for identification.