There’s an updated (March 2017) Premium Assurance datasheet from Microsoft. Premium Assurance allows you to add 6 more years of product support to SQL or Windows Server licences with active SA.
There’s a phased pricing model – the later you purchase Premium Assurance, the more expensive it is. The main adjustment to this datasheet is the inclusion of a TCO example showing that if you want to maintain product support for Windows Server until December 2026 it’s actually more cost effective to start paying in March 2017 rather than March 2020.
Find it here: http://bit.ly/MSLicensingGuides.