Conditioning the next button once all interactive buttons have been visited

Hi, I am new to Articulate and am looking to build some induction training having previously used Captivate.  I have a basic knowledge of the triggers and conditions in Storyline 360 but I can't seem to get the next button to work.  I have a slide with 4 buttons on that each go to different slides in the training and all returning to this one menu page, before then advancing through the remainder of the training.  I want to deactivate the next button until all of the interactive buttons have been clicked and pages visited.  I have:

• changed the state of the next button to hidden when the timeline starts
• set triggers to each of the buttons on the page to:
  • jump to slide XX when the user clicks
  • change state of the button to completed state when the user clicks
• then I've played with setting the slide trigger and the player trigger to change the state of the next button to normal when the state of each button is set to complete

This isn't working though, and the next button doesn't become visible.

I have found examples whereby the content for buttons is put into layers on the slide, but is it possible to do it with interactive buttons that take you to other slide content, whilst controlling the next button?