1 If your propane tank has been requalified, the requalification date will be printed on an oval sticker and affixed to the collar of the tank. 2  If the date on the sticker does not have a letter to the right of it, your propane tank needs to be requalified within 12 years of the date on the sticker.nstructions. Locate the collar of your propane tank. The collar is the raised piece of metal at the top of the tank, surrounding the valve. On the bottom half of the collar, look for the letters MFG DATE.. This indicates the manufacturing date.