We have desktop licenses with current SA, shouldn't we be able to add MDOP?

Question

We currently have desktop licenses with current software assurance. We would like to add MDOP, but our vendor tells us that Microsoft does not permit MDOP to be added because we purchased our licenses as Open Business + SA instead of Open Value +
SA.  This is quite a shock since all of the Microsoft documents I have found indicate that the only necessary prerequisite to MDOP is desktop licenses with SA.
Here is the applicable excerpt from the Microsoft Product List:
The MDOP home page reads "The Microsoft Desktop Optimization Pack (MDOP) is a suite of technologies available as a subscription for Software
Assurance customers."
There are no qualifications, exemptions, or asterisks in there.  Am I missing something? 
Is it really true that MDOP is only available for Open Value customers and not Open Business customers? 

Answer 1

Hi Falko,
If you open the Software Assurance Benefits: Entitlement Summary that you refer to, and hover over the Open License/MDOP
box, it reads "You may subscribe to MDOP when you have active Software Assurance coverage for the Windows desktop operating system."  It also makes sense that there is no checkbox for MDOP under Open License (and not the others) because SA is
optional for Open License (but included for the others).  We have
(the optional) "Software Assurance coverage for the Windows desktop operating system" and therefore according to that PDF, we "may subscribe to MDOP."  But, obviously, that PDF leaves a bit to interpretation and is, rightfully,
absolutely not authoritative.
The authoritative combination of licensing documents (and their precedence) are described in the License Stack blog post.  In our case, we agreed to
the license terms when we agreed to the Open License Agreement.  The Open License Agreement references two documents that mention MDOP:
the Product List
the Product Use Rights
Neither the Open License Agreement, the Product List, nor the Product Use Rights documents make any distinction between Open Value and Open License when referencing MDOP.  In fact,
the only prerequisite to MDOP stated anywhere is "Active Software Assurance for the Windows Desktop Operating System".
I just don't see what I am missing.  The authoritative licensing documents are absolutely clear: If you have Software Assurance for the Windows Desktop Operating System, you are eligible to acquire licenses for MDOP.  There is no distinction
based on how you acquired your Software Assurance.
Is there a licensing professional at Microsoft that could clear this up for me please?
Thanks for your help,
Alex