Where the MSI file is copied after the installation?

Does it not go into %windir%\installer\?

Though I think that the files may get renamed. Not sure where you get the name mapping from...

This directory gets very big so I move it to an external drive. This sometimes cause uninstalls or updates to fail with a missing msi error, but this can be fixed by putting the directory back.

Installshield creates a copy of all MSI files at %windir%\installer\ path. The WINDIR environment variable points to the location of the Windows installation directory. Typically it is C:\Windows. Before creating a copy of any MSI file it renames it using some random nomenclature e.g. I can see a file named 65ec5c99.msi in my C:\Windows\Installer directory.

Now to figure out the actual product name for the renamed MSI file there are two ways:

1. Check LocalPackage attribute inside registry at below path - [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersio‌​n\Installer\UserData‌​\<InternalUserId>\Pr‌​oducts\<ProductGUID>‌​\InstallProperties]

   InternalUserId is something of sort S-1-5-18. ProductGUID is a GUID like 00058CD18F0BF523DA1072073D56715D embedded as a public property inside the MSI file itself. You can get the value of this public property by opening your MSI file using any tool e.g. Orca

2. Open C:\Windows\Installer folder in explorer. Change the view of the directory to Details view. Add Subject column to the view. Now the product name of every MSI in that folder can be seen in Subject column (Refer screenshot):

   

Note: C:\Windows\installer is a hidden directory. So it is not visible in explorer by default. To make it visible, go to View tab in explorer > Click on Options dropdown button > Click on Change folder and search options > This will open Folder Options dialog box (Refer screenshot) > Click on View tab > Now make below changes:

• Check Show hidden files, folders, and drives option button
• Uncheck Hide protected operating system files(Recommended) checkbox