Slide Count: Omit a slide from the overall count

I suppose you have those variables on each slide? Use an advanced action to calculate the wanted number of slides to show up and store it in a user variable. Apply that action to each slide On Enter, which is very easy since you can select all slides in the Filmstrip with CTRL-A:

1. create a user variable v_count
2. create this advanced action:
     Expression v_count = cpInfoSlideCount - 1
     Continue
   
   

The text on the master slide or timed for the rest of the project: $$cpInfoCurrentSlide$$/$$v_count$$

Or you could simply type in the number of slides of course