1940's air mail from Switzerland

Expedited, registered air mail letter from Bern, Switzerland to Madrid, Spain 3.1.1942. Air mail route between Madrid and Barcelona was open already in 1927. All air mail from Switzerland was routed to Barcelona and continued to their destinations from there. This time the destination was Madrid and domestic air mail route was available. 

Cost of expedited shipping was 60 rappen, air mail to Spain was 10 rappen for each beginning 20 grams of weight,  letter rate abroad was 30 and the cost of registering 30 rappen. The 2 francs postage stamp (Michel 393) exceeds the correct rate.  The cover also has a block of four cinderella postmarks (Michel BIE III) of the International Bureau of Education (nowadays under the jurisdiction of UNESCO). These postmarks were used during the World War II when the bureau sent official mail concerning prisoners of war. These were normally not cancelled and so is the case here as well. The back of the cover has an arrival stamping 7.1.1942 so even if this letter was expedited, the war time route was not very fast having a delivery time exceeding four days.