Previous Data Protector 7 licenses

I have an implementation with previous Data Protector 7 licenses, which are not supported.
I damaged my library and I want to see if I buy new licenses for disk support about 4 TB, but I know that version 7 is no longer marketed.
You can downgrade the version 9 licenses or it is not possible and I have to compose all the licenses and make the migration to version 9