With each new release/upgrade/update of Windows there are changes to the group policy settings. ADMX files are of course the way Microsoft publishes most of these new settings and then we as GPO admins normally just update the Central store and we now (presumably) have a superset of the policy setting we had on all our GPOs. However, this is not always the case and Microsoft does occasionally modify and remove group policy settings. An example of this is the recent changes to the Windows 10 version upgrade policy settings which were removed and completely replace between Windows 10 1511 and 1607 (see http://www.grouppolicy.biz/2016/08/windows-update-business-group-policy-changes-windows-10-1607/) .
Historically Microsoft has release a new spreadsheet with each new version of an OS (see http://www.microsoft.com/en-us/download/details.aspx?id=48257 ) which is a good reference to have. But it was still very hard to figure out what settings had been created, updated or deleted from the past versions as there are many thousand of setting that needed to be compared.
Thankfully, Kai Ohnesorge a Premier Field Engineer (PFE) based in Germany has created a “ADMX Version History” spreadsheet that actually tracks all the new, changed and removed settings between versions ADMX files release by Microsoft dating back to Windows Vista. This will certainly be a handy reference guide for any GPO Administrator. For me, I think this will be most valuable when some Group Policy settings have just “disappeared” so I can actually check that this might have actually been the case.
To see the more information about this spreadsheet and for the links to download the file check out https://blogs.technet.microsoft.com/grouppolicy/2016/10/12/admx-version-history/