8 Sep 1937
Transit New York, 20 Sep 1937
Washington, D.C., Library of Congress,
21 Sep 1937
20g UPU letter = 1.75F
1F/add’l 20g x 2 = 2.00F
UPU registry fee = 1.75F
If you collect the officials, you know that the 5-franc p. 12½ Adolphe Bridge pictorial with the Officiel overprint in red did not appear until 1934, and that it is much scarcer than the p. 11½x11 version, which appeared 12 years earlier, in 1922.
The cover shown here was posted in September 1937 from the Office des Timbres Officiels (violet cachet), so unsurprisingly it bears the scarce p. 12½ Adolphe Bridge official.
But what is more remarkable is that the Officiel overprint is displaced to the very top right of the stamp. This variety is unlisted in Prifix and not mentioned in other references. Do you have an example in your collection?