Hi Paul,
Did you have active Software Assurance (SA) on your RDS CALs back when 2012 was released? If yes then you also have the right to use 2012 RDS CALs.
When you log on to your VLSC account, does it say you have 2012 RDS CALs, or only 2008?
If you are 100% sure you do not own 2012 RDS CALs via SA entitlement or similar, then I would say the behavior you are seeing is just the lack of strict checking by the wizard. I can tell you that it does allow you to make other similar mistakes,
like installing the wrong type (Per Device when you own Per User) of RDS CAL.
The critical point is even if RD Licensing allows you to install RDS CALs you do not own it does not make you compliant with the license agreement and Product Use Rights document. I recommend you verify whether or not you own 2012 RDS CALs and
if not purchase the required amount. One of the things you want to be able to demonstrate to an auditor is that you own the correct licenses.
-TP