Simplex Champion du Monde (GBA Italy 1st style) derailleur

In 1935 Simplex launched a single pulley, pull-chain, derailleur that went on to change the world. It was simple, relatively cheap to produce and mounted onto a standard dropout - so it could be fitted to virtually any bike. Inevitably, Simplex produced this design in a lavish range of minutely different variants and under a profusion of confusingly different names. Production continued for a remarkable 24 years from 1935 and 1959.

It would be remiss not to comment that these derailleurs were fragile, imprecise and had very limited capacity. But despite this they were a huge commercial success and did much to establish the derailleur as a standard piece of racing equipment. Simplex produced them in their hundreds of thousands, and, in the 1930s, marketed them by aggressively sponsoring leading riders to use them, establishing a pattern that persists to this day.

My best guess at a timeline for this design might include:

The series possibly starts in 1935 with the 'Simplex 35' which is a frequently mentioned model that I have not even seen in a picture!
Then, also in 1935, comes the 'Simplex Champion de France'. This most definitely existed, and was possibly a Simplex 35 rechristened to celebrate Simplex's victory in the French National Championships. It was a steel derailleur, with a long slot in the hanger for the dropout bolt. The sliding mechanism was also basic with the pulley bearing sliding directly along a rod screwed into the main arm.
You then see mention of a 'Simplex 36', supposedly dating from 1936. Again I have never seen this mystical object.
However, also in 1936, Simplex introduced the 'Simplex Champion du Monde'. This was named for Antonin Magne's victory in the 1936 World Road Race (using this very model). It was rather similar to the previous year's Simplex Champion de France except that the sliding mechanism was improved. The pulley wheel was now mounted on a long rod which slid inside a cylinder which was screwed into the main arm.
Sometime shortly after this, perhaps in 1938, but certainly by 1939, the hanger on the Simplex Champion du Monde was changed to be more 'normal' with a simple round hole for the dropout bolt.
At the same time Simplex released the 'Simplex Champion du Monde Extra-Léger'. This was an extra light aluminium version. Even here I am aware of two versions, both have an aluminium main arm, but one has an aluminium hanger and pulley cage, and the other uses steel for these parts. I have no idea which came first.
After the Second World War all forms of the single pulley Simplex Champion du Monde disappear from any Simplex catalogues. I think this model was no longer produced by Simplex in their main factory in France. Instead they went onto the double pulley Simplex Champion du Monde 46.
However, at this time, Simplex started to produce derailleurs in Italy. In Italy there was strong demand for a cheap derailleur for 3-speed utility and shopping bicycles, and the venerable Simplex Champion du Monde was just the ticket. I believe that the first model produced, possibly in 1946?, was a 'Simplex Campione del Mondo' produced in Milan by some kind of licensee or joint venture called ABML.
Possibly by 1947? the 'Simplex Campione del Mondo' was being manufactured by a different licensee or joint venture that went under the initials GBA.
Shortly after this (1948?) the name was changed back to Simplex Champion du Monde.
During the 1950s the quality of manufacture, and particularly the quality of chroming, improved markedly. The words 'Made in Italy' also now appeared on the derailleurs.
I believe that production of the Simplex Champion du Monde in Italy ended in 1959.

This is a very well used example with the following features:

The writing on the outside of the main arm is 'LE SIMPLEX TYPE CHAMPION DU MONDE'. The words 'LE SIMPLEX' are in plain capitals.
There is an oval 'GBA' logo on the inside of the main arm.
There is a logo made up of the Simplex 'S' in a circle stamped on each of the steel pulley cage plates.
The main arm is steel, plated and silver coloured.
There is no volute spring protecting the sliding rod mechanism. I believe that this may be original.
The hanger is steel, has a conventional hole for the dropout bolt, and is plated and silver coloured.
The pulley wheel has a black oxide finish.
The range control rod is 58mm long.
There is no ferrule around the toggle chain hole in the main arm, but the hole is extensively counter-sunk to ease the flow of the toggle chain.

In the main photograph I have disengaged the main spring to allow the gear to take up a more normal position.