I don't know when the phrase "em dash" got popular. It was probably due to web development, because, unless you were into typesetting, nobody knew what "em" was. We always just called them dashes--two hyphens make a dash.
The latter is barely used, but is the right way to indicate dates like 2023-25.
The more you know!
Some of us found out we were typography nerds and didn't know it until then.