Toilet Flange Install
All the flanges I have installed have set on top the flooring. If you place a straight-edge across the bottom of the toilet bowl, you will see that there is room for the wax seal under the discharge hole. Doubling up on wax seals can be tricky and if the top one slides while installing the bowl, it can block the flange hole. If the original flange will be lower than the flooring, buy an extender flange the proper thickness and seal it against the original flange and secure it to the floor using the 4 holes in the original and extender flange.
If you have never made a mistake, you haven't done much.