Always an interesting topic, this. I live in hope of picking up some old volume and finding fascinating annotations within, clues to the past, remnants of old lives. I've got a number of very old books - eighteenth-century editions of Tristram Shandy, the Rambler, and the original Spectator - but their previous owners seem to have been careful, reticent folk.
Looking back at one's own jottings is another matter. I think I last read Brookner's Providence in the 1990s, and I'm using the same copy for my reread. I find disappointingly few marks, and no notes. But the few marks intrigue me. I responded, back then, to passages that leave me cold now. I don't wish to go into too much detail here, but in general I seemed to 'identify' (hateful word, but unavoidable) more with Maurice than with Kitty. Now the opposite is true. As I say, interesting - but probably only to myself, so we'll leave it there.