Any unused/unallotted TQ quota gets transferred back to general quota. I will quote an instance here. I had booked a berth for my friend for today's journey from UD to SBC by train No:16524 which at the time of booking was RAC 24. Today morning, when I checked TQ quota, it was showing as 112 still available and I was sure that the RAC will get confirmed and was sure that even after alloting berth to all RAC, some berth may be available. So, when I checked general quota for today's journey, 20 berth is available which was unused TQ transferred. So, who ever wants to undertake journey at short notice and if chart is already prepared, please check general quota and book the berth if any berth is still available.