The extra button is correct. It's the "Recce Event Mark Switch" on the F-18C and "waypoint increment switch (WINC) switch on the AV-8B."
The slider is "extra" but I kinda like the idea of using it zoom control.
As far as I can tell, the only difference between the F-18C and AV-8B sticks is the Trim and Castle are swapped...otherwise the look like same stick. Hopefully, if a person wants they can swap the Castle and Trim switches to model whatever version the desire.
If I get a chance I'll ask next week at the Flight Sim show.