[Laurent Rizzotti]

If you compare fighter losses with fighter claims (including enemy fighter but also bomber and reconnaissance aircraft), you will find that most of the fighter units of WW2 would be "victorious", claiming more than their own losses.

In some unit histories, to reach this, the writer had to compare claims against the number of pilot lost in combat, that is usually far lower than the number of aircraft lost.

Peter Cornwell's "Battle of France Then & Now" is excellent for covering the air battles on the French border, but the North Sea battles are out of his scope and saw a great part of the German and RAF losses, so should be included in the total to see which side won... if any did.

My bet would be to search numbers in the old book "Fledgling Eagles: the Complete Account of Air Operations During the Phoney War and Norwegian Campaign, 1940", by Christopher Shores, with John Foreman, Christian-Jacques Ehrengardt, Heinrich Weiss and Bjorn Olsen.

Cornwell's has more details, especially on crew losses and distinction between damaged/destroyed aircraft, but it seems to me that most if not all combat losses of the period were already known to Shores and co at the time.