There is a group policy for saving password, maybe that is being applied: Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services\DisablePasswordSaving =1
We typically don't use file detection. In this case, registry:
HKLM:SOFTWARE\SolidWorks\SOLIDWORKS 2018\Setup
InstallSource = \\SERVERNAME\software\Solidworks2018\SOLIDWORKS 2018 SP4.0\64bit\SOLIDWORKS\
We are using the using the command line - "\\SERVERNAME\software\Solidworks2018\SOLIDWORKS 2018 SP4.0\startswinstall.exe" /qn
I didn't create this particular install app, let me know if you need more info and I can put you in touch.