Thanks cjoseph.
I wasn't sure based on a couple of paragraphs in the 'Aruba Mobility Master Licensing Guide'.
This one in particular...
'If a controller had previously installed sharable licenses before it was added to a Mobility Master as a managed device, those licenses are no longer usable on a managed device. These license keys must be added to the Mobility Master and then Mobility Master WebUI and assign them to the Managed node'.
Probably just my reading of it as when we ordered the licenses we had them assigned to specific serial numbers of wireless controllers.