My tellers save these bills for me as well and I take whatever they are willing to set aside for me. In a little over a year I probably have gone through close to $60K in the old bills. Most I have put back into circ, but needless to say with that volume there have also been quite a few gems that I have found as well. Silver certs, red seals, and even bills from series 1934 are still getting turned in.