Another very nice Ferrari Racing Set arrived today with an outside box but no internal platform piece. It's still a first class and quite rare item that will be on the main site soon. When I looked at this against the other set that had come a few days ago and was still lying around it was obvious that the trailers were different.
One is slightly longer and has wheel 'stops' set in at the front which are absent from the other. Underneath there is no different text. As far as I can tell the yellow trailer has only ever appeared in GS17 sets. There is red version in other sets involving a Maserati and the Lotus Racing Set but no other yellows. So, during what was quite a short life anyway for this set, a change must have been made. The longer one does hold the racing car better but the balance of the smaller one seems to ensure it stays attached so they each have their merits!
If anyone has more background about this do let me know.