Re: 2 wax rings on toilet install?
Usually use 2 rings when you have added a subfloor and now the toilet is setting up farther from the pipe than it used to be, or when the first ring has been smashed over time and there needs to be an extra ring added to keep things on an even keel. As LT says, you need to be very careful at seating the commode ... you don't want to crack the porcelan, and you don't want the wax ring oozing into the drain. Slow and gentle.
But yes, it will work when one will not work.