I forget which downturn it was, but probably 30-40 years ago (before it was explicitly made illegal), I'd see want ads with an incredibly detailed list of requirements that would terminate with something similar to "... or 6-9 months in the job offered."
What was happening was that they had either a college intern or a temp whose green card was about to expire who was performing acceptably, so they wrote up the position requirements based on everything the individual was actually doing, not the actual requirements for the nominal position, and put in that last phrase to make certain that the person they already had didn't have to document being able to meet the other requirements, and if someone applied who actually met the list of requirements, they could justify saying that they were making a justified business decision to hire the "less expensive" person.?
As a related aside, somewhere, if I haven't thrown it away, I have a 3x5 card to which I've taped one of those 3-line tiny classified ads asking for someone who is highly qualified in quantum physics and advanced MHD. I just thought it was incongruous to be looking for those types of qualifications with that sort of ad.