I need to run this all by Peter Cornwell, but it looks like we've made significant progress here.
A starting point for progress has to be the documented losses on KGr. 100's first operations from France. On 13/14 August - the first operational night - the Gruppe reported just
one aircraft lost, that which force landed at Pointe de Mousterlin. Neither Wakefield nor Ultra mention a second casualty.
The next operation took place on the 15/16th: one Heinkel was missing, one force landed near Dinard (north coast of Brittany), a third force landed near Bordeaux. KGr. 100 requested replacements for all three.
You're quite right that anyone coming down near Bordeaux was probably lost, having overshot their own base by almost 300 km. An aircraft returning damaged from a raid over England would be far more likely to set down on the northern coast of France, the nearest landfall.