Changing States across many slides with one variable?

Picking up on this older post, I have SL2 with 4 scenes. Scene 1 is an 'intro' scene and the last slide has 3 buttons for the student to select which topic to watch. Each topic has to be completely viewed (all slides in that scene), so I can't set a trigger on the button to show a completion check (hidden at start of slide) on click because simply using the button to go to the first slide of the topic scene does not mean they have completed the scene.

At the end of say, scene 4, I have a variable called Scene4Complete that changes value from False to True at the beginning of the slide timeline. When the student clicks the Next button they are returned to Scene 1 to the last slide to select another topic. I have a trigger that is set to change the state of the checkmark from hidden to normal when the timeline starts If Scene4Complete is equal to True. It's not working. The check is not changing states to normal. How do I get a variable that changes value in a different scene to affect change on an object in another scene?