I've been looking, and haven't quite found anything that matches my situation closely enough to satisfy me…
So, I just put down some vinyl plank flooring, and when going to mount the toilet again, I noticed that the guide for the one of the closet bolts was a little cracked, but I tried anyway. Using the fluidmaster "better than wax" waxless seal, I tried mounting the toilet, but the bolt guide broke further, so this flange just isn't going to work.
The issue is that the flange is under a layer of concrete, about 3/16" thick. It looks like we'd have to chip out the concrete on top of the flange to remove it, then fill the void, then install a new flange at the appropriate height. Is that the best thing to do here? I've seen stuff about putting a repair ring right on top of the damaged flange, but nothing I've seen said that was ok for a pvc flange. (Also, there is a bunch of duct tape sticking out between the concrete and the flange, so I don't know how well that would seal.)
So, I'm mostly asking what the most correct option is here. I'd like to make sure this is as code-compliant as possible, but I'm at a loss for how to begin.
Also of note: it looks like the sewer line is pvc all the way down. I don't know whether that matters at all …
… 
Best Answer
I would install a toilet Flange repair ring. This is a metal ring you mount on top this method cost about 10$. The other route is to cut the old flange out and install a new compression flange. This method cost about 35-40$ and is more work but the advantage is it works well with the new height of the flooring. Both methods work but I prefer the compression flange when changing flooring height.