Listen to recordings while looking at the score. I find that helpful.
It is easy to play a piece by flitting over the difficult passages and approximating the notes, and making up an interpretation on the fly. But is that what you would call knowing and understanding?
im lost what are you talking about ed and noah?
If you can play only left hand by memory from start to the end, you know it .
[shadow=red,left,300]No.[/shadow]This is what some important prof.s of piano recommend.Try it and see ...