Hi Gus,
The tunic has not been "assembled" by anyone other than the balloon observor George A. Spooner who wore it in France, to the best of my knowledge.
The explanation as to the different patina between the "US" insignia and the Air Service winged propeller devices is easy to understand if the facts are known about the two devices. The different patina is because the "US" devices are the seldom seen "Fire Bronze" type, and so marked on the backside. The winged propellors are actually made in France, and are a very scarce pattern, very rarely seen available on the market. Two different manufacturers of the two different devices, seperated by an ocean, and thus the difference in the patina. "Fire Bronze" devices always maintain an entirely different color patina, (almost a copper color look) as compared to the regular "bronze" coated devices which are typically a "Hershey chocolate" brownish color. I do have a single winged propeller device in my collection that is "Fire Bronze" marked, and it too looks entirely different than the patina on all my other sets and single winged propellor Air Service officer collar devices.
This uniform was aquired in Des Moines, Iowa in the summer of 1967 by one of my closest friends when he was a boy of 12 or 13 years of age. I did not get to meet him until 1981, and by that time he had aquired a wonderful Pickelhaube collection. He passed on in 1997, and I was fortunate to aquire this uniform from his estate. I have a photo of him wearing this uniform when he was a boy, and it looks quite sharp on him. He told me that he bought it at a garage sale several blocks from his home, and used his newspaper delivery money savings to purchase it. The uniform ensemble was the start of his military collection. Suprisingly there was another Balloon Observor who had resided at an address within 15-20 blocks away from where my friend had lived, who had served in the 9th Balloon Company with Spooner. I don't know for certain, but I suspect that my friend may possibly have aquired it from this other observor. But who really knows... That specific info is lost to the ages, unfortunately...
Here's info on Air Service wings/Signal Corps devices, and the dates when they transitioned from Signal Corps devices to Air Service devices:
J. Duncan Campell, who wrote the benchmark book "Aviation Badges and Insignia of the United States Army 1913-1946" states: "The mystery of this winged globe pattern (applied to the Signal Corps insignia) has been solved with the discovery of a mis-filed letter in the National Archives. The letter was sent by the Chief of Air Service, AEF, to the Commander-in-Chief, AEF, requesting authorization of a sketched insignia for "Air Service, Overseas." The request of April 18, 1918 was approved by General John J. Pershing on 27 April 1918. A second document found with this letter, dated 2 May 1918, from the Chief of the Air Service, AEF, is headed: "New Insignia for the Air Service," and includes a large drawing of the insignia. At the bottom of this memo is a notation by General Benjamin Fulois: "Notify all Sections and Stations of the Air Service."
He goes on to state: "This insignia, unknown and unheralded for almost 60 years, is most important because it is the first authorized insignia to identify the Army Air Service. It is excessively rare because few were produced in the short 80-day period before 17 July 1918 when the new Air Service wing and propeller device was adopted."
So that solves the inception date as to when the winged propeller device was adopted, 17 July 1918, when the Air Service changed from the crossed signal corps flags w/the applied winged globe device.
Hope this info helps. Thanks again Gus!
All the Best,
Alan