The ";" prompt was specific the "es" and "rc" shells, and not really used with any other more common ones, so most graybeards wouldn't have used that as PS1. Also, to be a graybeard and have copy/paste, you're talking about a very expensive computer with a mouse, like a Sun workstation. And all of those csh users from the late 1980s couldn't have, since it would cause a syntax error :-)
I remember independently inventing the ": foo;" prompt, and using it with Bash, in the late 90s. My beard is gray now.
It's not really practical because there are all sorts of values of "foo" which will make Bash choke when it tries to evaluate the string. Backticks and parentheses, for example, will cause problems, as will newlines (which NB may even occur in filenames, along with other problematic characters!). So the "foo" string typically needs to be sanitized using an external command: https://tldp.org/HOWTO/Bash-Prompt-HOWTO/x279.html
Once you get to that point the idea no longer seems as elegant.
