There are always exceptions to the rule. The Nivex parallelogram derailleur predates the GS by 13 years. But as the parallelogram derailleur was widely accepted after the GS, twin jockey wheel derailleurs were widely accepted after the TdF.

The circular black / gold graphic on the top pivot of your Simplex derailleur dates it to late 1950s I believe.

Dbakl, fascinating link you provided, racing pic and even an exploded view of the TdF. Gridplan, that is fabulous, and with the box, I am blown away. I had no idea I would get this depth of information. Thanks to all of you. Well, I was hoping to get a nice triple plateau crank out of the deal to make a nice steel touring bike. We will see. The worn out crap on eBay going for $150, unbelievable... I think the economy is not too bad for some.

I had one in my parts for 25 years. Finally was able to use it on the Atala I mentioned, which came without one.

Do you still have the derailler?