That’s a good question!
They are disposed of as the signage in the committee area indicates. The works shelves aren’t ‘storage’, they are essentially a tool. It has a lot to do with the stages where the progress of work is out of your hands. It can take a highly variable amount of time to move to each phase so it isn’t something community potters can precisely plan around. We give a nice sized window for folks to process their piece to the next stage/pick up from the final one. The key phases where one must act are for green pieces still in progress (waiting to trim, slab assembly, etc.), bisqued items awaiting glazing, and final completed items.
The absolutely best thing is to monitor the progress of pieces closely and get them quickly from one point to the next, making room for what is coming in behind. That’s the ideal, :).