[Spooky23]

We briefly had a 9-line party line at my parent's house in upstate NY in 1989. Their building of the house prompted the local bell to install private lines.

They lived in the country, but not in an usually isolated area. 100% of the areas in rural areas had these in that region until the late 70s.

Some of the infrastructure was just retrofitted to provide private line service. I saw wood based mechanical switches in production (in very isolated areas in New York) circa 1997.