I think people are forgetting something here. You may not forget how to ride a bike if you've had an amnesia, but you won't remember you know how to ride it until you try doing it. And even then, you'll just do it routinely. You won't remember how many times you fell while you were trying to learn, or how many years have you been able to drive. Look up some of those examples and see for yourself.
It would be an equivalent of Luffy still being able to use Haki, but not being aware of it. Or Brook forgetting he can actually play a violin.
But I'm just theorizing out of boredom. It's a drag having to read people explaining how the memory works to me.
Sorry it's a drag to be schooled, but your theories are kind of holey. We're just pointing that out for you. It's all in good fun, anyway.
Luffy was using haki a long time before he knew it. If he was using it instinctively then, then why not now? Besides, isn't haki all about instinct, anyway? Why would you have to have memories of training it?
And if Brook forgot that he could play the violin, wouldn't he be a little surprised that he's carrying one with him everywhere? Similarly, Luffy carries his haki training experience with him wherever he goes now, whether he remembers the training or not.