Yup! The strain relief cable clip greeblies have been found before though perhaps they have not been super widely discussed. Looks like you have found a vintage example, so that's cool! The ROTJ chest boxes do indeed use two of the larger side of the clips, flipped the opposite direction of the ones on the ESB chest boxes.
Hi all, If you wanna get these I found a link below by the maker of them (please correct me if these are somehow a slightly different version to the original)