You seem to veer off the rails all over the place, but the main thing that mystified me is - why would a label NOT WORK the next day (a "confusion" you list more than once)? It's insane to think it would not.
From the USPS Report on PRC Rate and Service Inquiries for December 2011:
You must mail your item on the date that you selected for your Click-N-Ship label; this is known as the Ship Date. An electronic record is generated on that date indicating that your mailpiece has been mailed. Packages shipped with labels that have incorrect Ship Dates may be returned to the sender and will not be eligible for a refund. If you are unable to use the label, you should request a refund within ten (10) days of the printing date and create another label with the correct Ship Date.
That said, local postal offices apparently offer varying amounts of flexibility; but the policy is that you must ship on the Ship Date or cancel within ten days to get a refund. See also here.