I have a vague memory of a computer (probably in the 16 bit era?) saving money on providing two joystick ports by using a DB25 housing with the middle pins removed, leaving two 9 pin clusters at the ends, into which two DE9 joysticks could be plugged. The case plastic covered over the middle of the connector.
Could well have been, though I’m still picturing a computer in my mind. Wasn’t the SAM Coupe, but that’s the sort of thing I’m recalling.
But: it was probably quite common on joystick interfaces, now you mention it. Thinking along those lines and searching for ‘twin joystick adapter’ let me actually find an example: https://www.ebay.com/itm/276075015721
Worth noting that in the image that shows two joysticks plugged in they really don’t look like they fit all that well…
