Thanks for coming on-line by your self, Lars. I do not remember if we have discussed this very a/c, but I was sure that you'd answered the question, if you had the answer - or included it in your articles.
If someone's interested : I have not yet entered to full list of operational sorties by Birksted from to ORBs at my website, but the this says that he was operational in FN-T for the first time on 16 June 1942
http://danishww2pilots.dk/pilotsSorties.php?id=15
Suppose you could be right about the guesswork. Wouldt it have had a painted Norwegian flag?!?
Mikkel