Hi,
In this forum, we mainly discuss technical questions about Office for Mac 2016.
Although it doesn't say it's a limited time offer, but based on my experience, if a user could upgrade from a previous version to a newer version, usually the user wouldn't get a new product key for the newer version.
However, it's my experience about some other products, not guaranteed.
I suggest you post the question in the Office for Mac 2011 forum, see if the engineers there are familiar with this topic:
http://answers.microsoft.com/en-us/mac/forum/macoffice2011
If no, you may need to contact the local customer service for this issue:
http://support.microsoft.com/gp/customer-service-phone-numbers/en-us
Regards,
Melon Chen
TechNet Community Support
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