Old Henri Selmer trombone identification

[ksdaddy]

I recently purchased a few dozen instruments at an estate sale. Mostly guitars, but a few generic newer trombones and a couple trumpets. One of the trombones appears to be quite old. There was a luggage tag inside the case with the name and address of a local man who I had met on many occasions. He graduated high school in 1947; I found his band photo in the yearbook. I don't see any model name anywhere, only the number 430. It does say "GRANDS PRIX" and I have read that some Selmers were known by that name. I also read it was very difficult to determine the manufacture date on these. Any information you would be willing to share would be appreciated.

[UATrombone]

"Grands prix" isn't model name of trombone.
Below are names of 2 cities with years of exhibitions, where and when this trombone model received Grand Prizes.