I was puzzled when I got these for my Super as well. The seat on your Beetle has three mounting points, one slides into a guide in the center front, and the two back ones go into those guides on the floor, which are the tracks.
The two that slide into the tracks on the floor are supposed to have an upper and lower piece of metal that sort of takes-up-the-slack between them and the tracks. If and of these are missing (there are 8 of them, two on each point) you'll get a wobble. Note, these are no longer available and are replaced by these one-piece spacers. You just slide these on, making sure that the old ones are not on there and your wobble will be history.