but ... what's the difference between being capable of playing well a certain piece possessing "certain" technical demands, vs. one's overall technical ability having reached a certain overall level? Is it just a matter of mentally being capable (or not) of recognizing where demands in one piece relate to another, and then to be able to carry it over?
So, yes, maybe you don't know precisely how to carry over thirds, but playing well the piece where you learned them means you can play a bunch of pieces "below" it.