[CJE]

Here I am, Graham!

We start from the "escadres" (roughly "Wings"). They had two or three "groupes" numbered as follows (roman numerals):

2e escadre de chasse :
GC I/2
GC II/2
GC III/2

31e escadre de bombardement :
GB I/31
GB II/31

Right?

Then, each "groupe" had two "escadrilles", numbered from 1 (arab numerals) on.

GC I/2 : 1ère and 2e escadrilles
GC II/2 : 3e and 4e escadrilles
GC III/2 : 5e and 6e escadrilles

Still following?

But... the "escadres" were disbanded as such in November 1939 and the "groupes" activated after numbered their "escadrilles" differently.
So, GC III/1, the "escadrilles" of which should have been numbered 5e and 6e escadrilles, numbered them 1ère and 2e escadrilles instead, because GC III/1 was activated in January 1940.

Have another glass and relax.