Hi,
Thanks for highlighting this.
To clarify, as per documentation ... "Office for Mac 2011 Volume License copies are required to apply IRM protection to files.
Office for Mac Home and Business 2011, Office for Mac Home and Student 2011, and Office for Mac Academic 2011 can only read files protected with IRM.
"
Ref Link
So all versions are effectively IRM enabled.
About upgrading the retail licenses to volume licenses, don't believe it's possible, but have a chat with the distributor or a licensing advisor to provide you with more accurate answer.
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