The first two digits represent the year, for example, 08 is 2008, and the last two digits represent the month, for example, 06 is June, and 0806 is the contract in June 2008.

The serial number is the date of delivery, which is expressed by the date of this year. 0806 is a contract. In June 2008, the 0806 contract was delivered and the 0806 contract expired. After delivery, the contract will fulfill its mission.