Guys
It seems like RAF was not all that fast to implement the new code system with the units in 1940. From the books I am reading it looks like it more or less came as a surprise to many units that they had in fact changed codes.
The so called pre-war code were
GR : 92 Sq
QJ : 616 Sq
At one point the top brass changed all pre-war codes to new ones and
GR became 301 Sq
QJ became 92 Sq
(616 Sq received YQ)
I don't believe there exists any official documents stating exactly WHEN the change took place. If it did there would be no problem at least not officially.
My own opinion is that with everything like new directives regarding markings, RAF in the field had their hands full with much more important issues than re-painting aeroplanes during the summer of 1940. They were in the middle of either winning or loosing the war! I have no problems seeing aeroplanes continuing to wear the pre-war markings for a much longer period than stipulated while getting new aircraft correctly painted.
Now on the other hand if someone has a 100% certainty of the date each and every photo he holds in his hand was taken, start shooting...
Cheers
Stig