If there are any issues installing .NET Framework 4.6 on Windows 8.1 or Server 2012 R2 because KB3919355 is not installed, ensure that the following prerequisite updates are applied before installing KB3919355 .
- May 2014 servicing stack update for Windows 8.1 and Windows Server 2012 R2
- Error 0x80071a91 when installing update 2919355 in Windows
While you're at it, you may as well recommend they apply the following updates afterward to get the latest Windows Update Agent as of June 2016 installed as it will prevent windows update from using unnecessary resources and also make getting the system up to date much smoother.
- April 2015 servicing stack update for Windows 8.1 and Windows Server 2012 R2
- July 2016 update rollup for Windows 8.1 and Windows Server 2012 R2