This blog post was written by Mark Empson, who is a Premier Field Engineer based in the UK.
Back in 2013, I started to uncover some challenges around upgrading ADMX/L files in the policy definitions folder (be it Local or in the central store) and the ramifications of some of the changes that can occur, with later revisions of the files. I initially put together a spreadsheet at the time, that looked at how the physical files changed between builds by using MD5 hashes of each released file and a direct comparison between only two builds of ADMX releases, to visualize the differences. This work was built upon by Kai Ohnesorge, as he took that work to the next stage, by documented all aspects of the content changes between all versions of the files (as can been seen on this blog site, via this link https://blogs.technet.microsoft.com/grouppolicy/2016/10/12/admx-version-history/ ).
Today, marks the release of a new knowledge base article that explains the known issues that could be experienced, while upgrading the PolicyDefinitions folder from a Windows Server 2012R2 build, with later version of ADMX files and it also explains how to mitigate those known issues. This document is also important while using the Advanced Group Policy Management (AGPM) server, as the same issues will also be visible.
This KB article 4015786 can be found on any of the links below:
Special thanks to Ajay Sarkaria, who is the Supportability PM for Group Policy and Kai Ohnesorge, who is also a PFE.