Tate, fascinating question and interesting answer. Normally you and I are so far apart on the way we approach character that we could be living on different planets. In this case, how we get there is just as far apart, but the end results are very similar.
Short answer, I don't keep track of any of those things unless they're directly germane to the plot.
Longer answer, I deal with characters in much the way a director deals with actors. There's a script. They follow along. If someone wants to know what their motivation is, I make something up and then go back and layer it into the early parts of the story. Say that on page 138 it becomes important that Johnny is fanatically attached to the color blue and that impacts the plot in a way I hadn't thought about in the original outline. I write the scene on 138, note the new twist down in my constantly updated plot outline, then go back and look for places earlier in the story that I can introduce the idea of color attachment, both personally for Johnny and thematically for the story.
Now, say that the character of Johnny wasn't actually fond of the color blue. I've rewritten his history at this point, so now he is. Simple as that. I hired these people to play certain parts. If that doesn't happen, they're out looking for a new job while a new actor comes in, identical in every respect but the fact that this one will do the job.
Does that mean that nothing off script happens? Of course not. If an actor improvises something that's cool and that moves the main story forward (the story I wanted to tell from that get-go, since that's how I write) I use it. Whole chapters have been born this way, and huge important new sections.
Of course, all my characters are really sort of like little split-off bits of myself since I don't actually believe in their independent realities. It's all a matter of "if I were this person in this situation..."
So, if it's critical to the story it goes in the plot outline. If it's merely a telling detail, I just store it in memory as it comes up, I can always do a word search if I lose it. If it's not that important, I don't generally know or care. It's all about what move the story forward.
I'd love to hear what other writers have to say on the subject since Tate and I, so far apart in conception, are so close in practical execution.
Anybody? Anybody? Bueller?