Recently a work client asked for a patch on functionality to a .NET4 app which now requires .NET 4.8. That app in turn uses a DLL which also also needs to be recompiled from source.

That DLL was last built in 2007. We've gone through three version control systems, multiple servers and backup systems, and at least two office moves. No one in the company, save the owner, has been here since 2007.

You might be getting an idea of this issue here.