I totally don't know what that is, but I see now. Is that just another part of the model number?
They're probably just different model years. The ergodyne line saw a lot of changes in its lifespan, and there are different variations of EDB's out there.
Composite Aficionado

Spector and Markbass
Ibanez tends to change the control layout and other minor detail couple of years in a models run.
Damn it! Disable can't use disable to disable Disable's disable because disable's disable has already been disabled by Disable's disable!