. . . so that a slide interaction on a slide that has the click-to-reveal widget can depend on whether all the cards in the widget have been click.

This is because the forward and back buttons are much more prominent than the "X" in the top right of the revealed card. Users don't see the "X" and mistakenly click on the back button instead trying to return to the front of the card. If you have completion status for the click-to-reveal widget, those buttons could be hidden until the user has clicked on all the cards.