I heard from internal sources that BB plans to increase the amount of used games in stores by 60%. Apparently, the company that handles the games once they are traded in has an overload of games at their warehouses that are going to be in stores by February
I'm not sure about that though you are correct that the previous company could not keep up with the volume. Would be awesome if they were just sitting on a bunch of games and starting getting those back in the stores.
The amount of used games a store will stock is dependent upon how many are traded in and how many used games are sold at that store. They also put into account how many trade ins a store takes compared to how many games (new and used) they sell. The average store has to take in 5-6 trade ins a day to hit the expected goal. On top of that they compare it to the district so if other stores are killing the store you go to in trade in units/% and used game sales then maybe less games going there. There is also no indication if its measured but popularity for the games or number of units (if 1 copy of MW3 is equal to 5 random PS2 games or something).
There is no exact formula they are admitting to but they put all of these things into account. Store I'm at has been averaging 1st-3rd in the district in both trade in units/% and used games sold and you can name any game released since August and we've had it used though its a bit uneven. We are sitting on like 10 Batman:AC for PS3 but only seen 1-2 for xbox but on the contrast we constantly in stock with MW3 for xbox but only had 1-2 in for the ps3 ever.