Next/previous buttons

In this case, I typically rely on triggers and variables to make the Prev/Next buttons active or inactive. How I do it depends on how my layers are set up (e.g., if they must be visited in order or if they can be visited in any order). Here's my setup if they can be visited in any order:

Each slide layer has a variable associated with it, and when the layer is visited a trigger sets that variable to TRUE.

The base layer has a trigger to disable the Next button at the start of the timeline IF those variables are false.

Each additional layer has a trigger that will make the Prev/Next button active at the start of the timeline if all those layer variables are true. That way, in case they revisit the base layer, it will still do a check that all layers have been visited and allow the person to navigate forward at will.