Do you keep a table tennis notebook? I did for years, and I recommend you do as well. I used a steno notebook. From front to back, I would take notes on my own game - what I was working on, what drills I was doing, what worked and didn't work in matches, etc. On the other side - back to front - I kept tactical notes on opponents. When the side on me was filled up (it usually went first), I'd get a new notebook for my game and start fresh. At tournaments, I'd bring past notebooks (with the ever-growing notes on opponents), and would be ready against any opponent I'd ever played against.
After doing this for perhaps a decade, I realized that I'd been doing it so long that notes about opponents I’d played were all in my head, and that I no longer needed to consult my notes to remember them – but the very act of writing them down made it easier to remember. I eventually retired my notebook in regard to tactical notes against opponents – though I sometimes would write down the notes as a memory aid, and then put them aside – but for years afterwards I kept notes on my own development and what I needed to do to improve.
These days you might use a smart phone for such notes, or go old school with a steno notebook. It still works!
While I no longer have a notebook for my game, I still keep notes on regular opponents of players I coach, which I jot down at tournaments and later type up in my coaching files on my computer. When I show up at major tournaments I bring these top secret printouts.