Yes. I once interviewed a developer who’s previous job was maintaining the .NET application that used an Excel sheet as the brain for decisions about where to drill for oil on the sea floor. No one understood what was in the Excel sheet. It was built by a geologist who was long gone. The engineering team understood the inputs and outputs. That’s all they needed to know.
Years ago when I worked for an engineering consulting company we had to work with a similarly complex, opaque Excel spreadsheet from General Electric modeling the operation of a nuclear power plant in exacting detail.
Same deal there -- the original author was a genius and was the only person who knew how it was set up or how it worked.