If memory serves, Matteo's Falerio Masi recently for auction on ebay had a Super Record rear derailleur with a Patent 73 impression on the top black body. There was one other for auction recently by vintagebike_76 (A. Nati) that was marked the same, it was actively pursued.
I remember the LeCycle article about that show that someone brought into the bike shop, there were lots of things that appeared in trade shows that never arrive to production. One of those shows in the 70's had TA Professional cranks with black chainrings and a titanium axle...
John Jorgensen
Palos Verdes Ca