From what I learned sounds like the buffers do outside AND INSIDE the tire leaving mostly just steel from belts and perhaps the rim. THEN comes the cryogenics which makes sense the cryogenics can't be to cheap to run. The less handling the cheaper the freezing process to my mind. Someone correct me if mistaken, appears the buffing strips the majority of the rubber from steel belts.
Therefore stockpiling some steel belts shouldn't pose a problem.
If you scroll down and check out the videos at the website below, you'll see the grinding/shredding part of the process. The tires then go through the separation process removing the wire and then further grinding/shredding to create nuggets and finer rubber.
Just a guess but these 4 buffers will give us revenue of 4 million a year, we have contracts for 18 million in buffings a year, so i,d say we need a total 16 buffers maybe