Prior to WW1, Cameroun was the German colony of Kamerun. Shortly after the outbreak of war, it was invaded by both British and French forces, with the main port Duala being occupied on Sept 27, 1914. The final defeat of the German forces took awhile but was complete on February 18, 1916.
Both the British and French issues stamps for Cameroun during the war, the British overprinting German Kamerun stamps found on a German ship captured on the way to Cameroun and the French overprinting stamps of its neighboring colony of Gabon. Of the three different sets of overprinted stamps issued by France for Cameroun during the war, the second set is the most difficult to find, especially on cover.
Thus I was pleased to purchase the following cover, postmarked 2.6.16 (June 2) and franked with five stamps from this set.

On the reverse is a receiving part from

But after looking at it for awhile, there are a couple of things that bother me about it, apart from the unfortunate folds.
1) Was the 50c stamp on the cover when it was mailed, or was it added later to "improve" the cover? Not that it actually does "improve" the cover -- according to the Maury catalog of French African colonies, the 5c stamp has a higher catalog value on cover than does the 50c stamp. But the cancel is very unclear, unlike the others, and, if looked at closely, is at a very different angle from them.
2) Regardless of whether the 50c stamps belongs on the cover or not, what rate were the stamps paying? I cannot find any rate for which either 12c or 62c would be the proper charge. Someone has suggested to me that this might have been part of a group of covers that together had the entire set of 14 stamps on them. Possible, but
this combination as part of such a set of covers seems rather odd.
Any ideas or comments?