Variable Triggers not triggering from variable in different scene

Michael is right, Adding to a total as you go along is fraught with so many possibilities for error. Whatever it takes, even if it requires creating a variable to record if each scenario has been completed, it's worth it. You could create a T/F variable for each scenario and change it when the last slide is finished which (as Michael pointed out,) must be changed before the jump to ... trigger. Then, when it is time to know if all scenarios are done, or how many are done you can write each one into a trigger condition, or count them. For example:

[Trigger activity] when [user takes action] if Scenario1 is true AND scenario2 is true, etc.

Or Add 1 to total when [user takes action] if scenario1 is true

Add 1 to total when [user takes action] if scenario2 is true  with each scenario needing its own trigger.

It's the best and most reliable method of knowing when you get to the end, because at no point is it vulnerable to user action.