StoryLine360 Next Button Enable/Disable based on slide being already viewed

Hello, I've created a project where I have the player's Next button disabled until the timeline finishes on the current slide (for each slide in the project). However, when a learner comes back to a previously viewed slide, they are forced to go through all content on the slide until the timeline ends again, before the Next button is enabled. I want them to have the ability to go back to review content, then skip back ahead to where they left off without the need to complete everything on each slide again. I know how to do this if there is interactive content such as buttons on slide that the learner needs to interact with using states, however I don't know how to do this when the slides only have text-to-speech that the timeline has to go through before the timeline end is reached to then illuminate the next button.

I was trying to use standard triggers without success, then I tried to create a variable, however it appears like I'll need to create a viewed variable for every slide individually since variables are carried through the entire project unless reset through another trigger. With the project having many slides, I'm hoping for a way to quickly set the previously viewed status for the individual slide so the next button was immediately available. Any thoughts on how to do this quickly? Thank you in advance for your advice!