Not just Bob, but any producer would weigh costs. Is it cheaper to box up, securely store, and fish out unused panels or just create a new one when needed? I would guess there were extra sets that were retained, or a few weeks' worth prepared in advance, but to have a whole library of them is probably more trouble than it's worth.
On the other hand, there was the unwritten rule that they would not flip to reveal a new box if there was 1 or sometimes 2 seconds left on the clock. So there was a deliberate recycling tactic in play, if only for the written game material, but possibly for the physical media.