I'm curious, is there a documented case of this having ever been an issue?
As in someone taking action for the violation? I'm not sure.
In the case of anyone's rights being transferred, yes.
Here's an easy one: Every developer in the US signs a paper in their offer transferring all IP and rights to the company. Sometimes it requires using their equipment/time, other times it's a blanket transfer of everything you produce is theirs.
You wrote an article here on a company laptop? Well, that is your company's property now.
As for more writing specific, my writing teacher has dealt with this at various points in her career. Many authors actually purchase rights tracking software. It becomes unwieldy to remember what you wrote for whom and what you're allowed to re-use or not across many years.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.