New Subscription Problem

In February I bought a new computer and installed NIS on the computer from a disk.  This month I bought another new computer and installed NIS on the computer from another newly purchased disk.  I used the same account for both computers.  Now my new computer coverage expires the same time as the computer I purchased in February.  What did I do wrong, and can I fix it so that my new computer has a full 365 days of coverage?  Thanks!