When I was young and played all the time I had multiples in multiple stages of wear, but it wasn't due to a rotation thing. It varied from disc to disc, but most discs would beat out the LSS first, so the discs faded less and straightened out. Usually I would beat the LSS out of 2-3 more discs before the original one would lose enough HSS to be considered a turnover disc, so there was always a backlog of seasoned discs ready to go. Eventually you would beat enough discs into turnover discs that you would have a stack of those going as well. You just naturally ended up with extras that way, you really didn't have to rotate discs in and out specifically with the intent of creating backups.
That is a really good point. A disc can go from "fresh" to "beat in" pretty quickly for me (I do throw primarily Trilogy, after all) but then it's about 2 years to get it from "beat in" to "turnover disc" or "thrashed." having played less than four years, I only have a couple of discs that have gotten past what I'd consider a normal beat in stage.