I do agree.MS RDS CALs do not have a hard limit.I think it is telling you that you have exceeded the license count by 28 CALs.
Obviously, if you upgrade to Server 2916, you'll need to replace the 2012 CALs with newer ones. That being said, it doesn't much matter whether a 2912 or 2916 RDS cal is assigned here, as long as you have rights to the number of users you will have log in, and assuming you stay on server 2912. So, you may have 17 licenses, but it looks like you have way more users than that connecting, evening though it may not be concurrently. You start the RDS License Manager and expect to see the number of issued client access licenses (CALs). Only in the case of a licensing audit is this count verified and enforced. You have a Windows Server 2012 R2-based Remote Desktop Services (RDS) license server. They also do not have a hard cutoff when it stops issuing connections, meaning they function similar to Server CAL's in that you need to be honest to the licensing agreement and make sure you have the right amount purchased and applied.
Per user CAL's are per named user, not per concurrent user.