After running an inventory, we found this installation: Microsoft Office 2011 Standard With Lync (Mac). We had purchased Office 2011 Standard for Mac through volume licensing and used the corresponding installer. Now, do we need to purchase Lync licenses?
No, you do not have to buy licenses for Lync, since it was included in the purchase of Office 2011 Standard for Mac through a volume licensing program.
Source: official Microsoft Website (https://www.microsoft.com/mac/enterprise/lync), retrieved 2015-08-06