I'm using the latest MSVC Redistributable package, 14.29.30037 as an EXE bundled in an NSIS setup file. With former versions, running it with the "/quiet /install" options has always produced the correct result: If an earlier version, or no version at all is present, install, otherwise there's already this version or a later one already installed, in which case do nothing.
With the latest, running "VC_Redist.x64.exe /quiet /install" winds up breaking the current installation. After doing this, any attempt to run a program that needs the MSVC Redistributable results in one or more dialogs stating that various DLL's are missing. Running VC_Redist.x64.exe with no arguments and selecting "Repair" restores to correct operation, but this is not a viable long term solution.
Edit --
For the time being, I've gone back to an archived copy of the 14.28.29334 MSVC Redistributable for building installers. This works with what I have now, so I can proceed. Needless to say, I will not be upgrading Visual Studio except on a sacrificial test system until this issue is resolved, since I need something that can continue to build executables that will function with a slightly out of date Redistributable.

