@Squatpushpull my current thoughts on it below. I currently do Time ID + Title (e.g. "202006011558 Metacognition).
So this is why Luhmann used an index combined with structural linking (notes 1a, 1b, 1c are structurally/thematically linked together) and direct links (e.g. writing “see note 1b” in the middle of a note). So he would use the index to get as close as he can to the topic he is thinking about, then manually go through the notes until he found what he was looking for. This is what you’d have to do unless you give every note a unique tag, which is essentially a secondary title.