There is a cognitive bias toward adjusting one's past to one's present. So if I learn something today, then a month from now it will seem like something I've always known. For example, I learned recently the the Walloons of Belgian are Francophone, or sometimes speakers of their own, Romance language. I had never known what they were before, and somehow had it in my mind that they were the opposite: speakers of Flemish. I'm sure a year from now I'll think that I always knew who the Walloons were.
On the piano, I cannot really remember exactly what I was playing a year ago, so I think of it, vaguely, as more or less what I'm playing now. Yet my teacher says I am greatly improved, and I probably have. We can shortchange our own progress by failing to remember correctly our past competence (or lack of).