It looks as also for some international parcels sent according to a bilateral convention the receiving country got a part of the postage. On
http://www.worldlii.org/int/other/t.../1923/19.pdf you will find the convenmtion with Sweden 1922 and there the followin is said in Article 7. "The Post Office Department of Sweden shall pay to the Post Office Department of the United States 50 centimes. (gold). for each parcel forwarded from its offices to the United States and the Post Office Department of the United States shall pay a similar amount to the Post Office department of Sweden for each parcel forwarded from its offices to Sweden.. The accounts shall be balanced every quarter and a general balance of such quarterly settlements struck yearly which amount shall· be paid by the Post Office Department of the debtor country" 50 gold centimes was then about 10 US cents