I've tried raising this with Snow Support, but they are not interested so I thought I would share here so that more people are aware of this issue.
From Windows Server 2008 to Windows Server 2012 Microsoft simplified their licensing structure down to 2 main tiers, Windows Server Standard and Windows Server Datacentre. The downgrade rights are:
However, Snow's upgrade / downgrade system is programmed on an edition index-based logic, and they have given Windows Server 2008 Enterprise a higher index than Windows Server 2012 Standard which means that if you have 100 Windows Server 2008 Enterprise servers and own 100 Windows Server 2016 Standard licenses, then your compliance will still show -100 unless you manually specify the downgrade. This is something that could be easily overlooked by users not familiar with Windows Server licensing.