I don't think many would have come with them from factory, but you can fit new universal sash belts. No need to go retractable. But once you fit them they must remain. Legally, if they weren't fitted they need not be. Passengers cannot be fined for not wearing a seatbelt that was not fitted from factory.
Some people play hard to get... I play hard to want...
I was under the impression that only front seat belts were optional, ans that they didn't come out with rear seat belts at all. I just used the rear lap sash belts out of a couple of KA Lasers on mine to put rears in.