Right now it's just two for me, but I rely a lot on the notes section in my tracking app that I've had since the start for logging doses, vial switches, how much solution I added, and how each one felt or didn't. The iOS version lets you add custom entries for anything, though the Android side hasn't added that option yet.
I've been looking into various peptides and combinations, and it strikes me how simple it is to lose track of which one is responsible for what, particularly if something shifts. When effects appear, it's tough to know if the latest addition caused it or if it's from everything together. Do most people introduce them separately to evaluate each on its own, or is that not a concern?