You own as many serial numbers (licenses) as appear in your My Account/My Software page. It doesn't matter which license you put in service as long as you obey the terms of use.
If you wish to assign a particular license to another user, I've heard that you must contact SCS to take care of that. I too have two DVD-A Pro licenses - one from VP 10 and one from VP 11. Still debating on VP 12.