Yes Daniel (FRENCHTRAINS)......the early manufactured Buco wagons had a "riveted" coupler connection (fine steel pin squashed at its end to retain the drop link coupler) where-as the more recent examples (from about the 1970's onward) had a small threaded pin and nut to secure the coupler. This is the easiest way to define the manufacture.
I believe it was in this change-over period that the lithograph lettering changed from yellow/gold to white, as shown in your examples.
Many spare parts are still available directly from Buco Spur O GmbH (https://buco-gmbh.ch/) as well as from Erich at Amiba Lokschupppen (https://www.amiba-shop.ch/Ersatzteile/Buco-Spur-0/)
Peter.....Buco Australia.