I know they double the gaskets up sometimes for uneven floors, if the flange is recessed down even with a tile floor, etc. It might possibly have a crank somewhere underneath or in the water channel.? Not sure if you can unhook it and look under it.
I have seen toilets that have been in service for years and then start to leak. On one, I found a small hole at the rear of the bowl near the top under the rim on the outside. When flushed, the rim water would flow out the hole and stop when the toilet was done flushing. A dab of silly-cone fixed it.