Now, now...just cool your heels.
First, not all memories are created equal. Mine is not so good. I am not sure what the difference would be between having an ECO in your lap vs CPT. Same deal, just one is paper and one is not. Actually, if I printed an opening I am trying out from CPT, it's absolutely no difference from looking at an ECO.
I used '17 half moves' below as an example. In a Dragon, that doesn't even get you to where White castles let alone near the end of theory where you actually get to start 'playing'...rather than remembering and blatantly repeating what others have done. It got me part of the way.
Oh, and it was ever just offhand games, no tournaments and not rated. IE: chess for fun. The way it is supposed to be.