https://www.cnet.com/reviews/sony-playstation-classic-preview/

The original NES and SNES consoles had unused ports like this, too -- but Nintendo didn't include them in the Classic Editions.

That extra level of detail carries over to the PlayStation Classic's controllers, too. Overall, they're pretty basic gamepads: simple, but excellent replicas of the PlayStation's original controllers. They feel right in the hand, and the separated PlayStation D-Pad and face buttons feel authentic -- but my favorite thing about them isn't the gamepads themselves. It's their connector.