I have a friend who has a vinyl record collection numbering upwards of 20,000. I once asked him how many Rolling Stones records he has and in about 0.7 seconds he replied "86".

I for one, am not that obsessive with keeping inventory, be it mentally, digitally, or hard copy. Maybe if I had a reason besides for the heck of it, like to make sure no one's getting into my stash, I'd some sort of database system, but for now, it's just footloose and fancy free.