My interests are mostly related to the US censorship of the WW2 period, but I've seen enough of the other countries censorship to be dangerous.
The two labels with the P.C. 90 are British censors, probably either Great Britain or maybe Bermuda, which had a large operation covering a substantial portion of the Western hemisphere to Europe mail. The large four digit numbers identify a particular censor, and in most instances, each individual censor used an assigned number all the time. If I recall, many of the labels used in
(corrected to) Jamaica also had a "IE" in front of the examiner number.
Edited to add: Bermuda had "IC".
I think (but am not positive) that these numbers were fixed in location of use and person using them. There is a database somewhere that lists many of these by number, label type, and where that number was used.
The French label also has a series of letters - not fully legible in this example - which represents a specific censorship office (see link below to find a list). I believe May 1941 is after the fall of Paris and partition of France into German occupied and Vichy France. As Bordeaux was in German territory, I suspect this letter reached Vichy France, but could not be sent onward to Bordeaux, even after censorship. Thus it was returned.
Hopefully an expert in this European censorship period can chime in and correct any of my statements which are in error.
Additional Edit: This is one site I found a while back with a considerable amount of detail on WW2 censorship.http://o.lafarge.free.fr/php/accueil_eng.php