Having the transmit/receive clock pins present was *reasonably* common on CP/M/S100-era computers. (The NorthStar Horizon has them, for instance.) Quite a few early machines also used some of the extra pins to provide for running 20ma current loop interface devices, but this wasn't an official part of the RS232 standard so a cable set up for one machine wouldn't necessarily work on a different one.
FWIW, the original IBM Async Communications Adapter card for the 5150 falls into that latter category, it uses pins 9, 11, 18, and 25 for the 20ma loop capability. So far as I know this wasn't commonly replicated on clone cards, and of course it went out the window with the 9-pin standard.