Your installed Plesk version can be inspected in the customer service center:

Plesk license version 8 is valid for all versions from 8.x.

Plesk license version 9 is valid for all versions from 9.0 to 9.4.x.

Plesk license version 9.5 is valid for all versions from 9.5 to 9.9.x.

Plesk license version 10 is valid for all versions 10.x and 11.x.

The Plesk license will be extended/renewed automatically after installing on the Plesk admin interface.