You are correct. The iControl library is the client proxy stubs for a specific product version. Let's say it's at 9.6.0 as of the latest release. Then it will support all versions of BIG-IP up to 9.6.0 with the methods that are available on that product version. If you have a version 9.0 of BIG-IP there is no way a client library can magically make server implementations appear for methods that are not implemented on the product.
As for upgrading, that will depend on your support contract. You'll have to go through the normal support channels to request a product upgrade.
-Joe
Nimbostratus