It appears that there are 8 magnets in the Morph, and 12 in the overlays (at least sometimes).
6 Morph magnets are the rectangular ones (4 top, 2 bottom), and there are two circular ones in the bottom corners. Along with holding the overlay in place, the N-S alignment of the magnets means that overlays cannot easily be installed spun around 180˚ and stay in alignment. A well thought out design.
In the magnet diagram it shows 4x additional single pole (aligned to the surface) circular magnets in the Innovator Overlay just next to the magnets in each corner. The left-hand ones are N-poles, and the right-hand side are S-poles. I’d guess those are what communicate the overlay’s ID to the Morph. If it’s detecting N/S/no-magnet at each of those spots then the number of possible unique overlays would be 3^4=81
