I think, Jhieminga, that nearly everyone is out of their depth in this particular pool. Even the acknowledged experts, on a French aviation history forum I frequent, presently are seeking help concerning two hitherto unknown French WW1 hydravions. However I think it fair to say that there is a connection between Donnet-Lévêque and the Maagen III - but what is far from clear is the number of links in and the length of the chain that connects them!