Hi Stig,
I'm not sure what sources the MAW team used. However, the 24 November 1942 strength return notes 6374, and the loss report submitted 8 January 1943 also notes 6374. The Germans might have made the same typo twice and typed 6374 rather than 6347, but that seems a bit unlikely.
However, I know very little about the Bf 109, so hopefully someone more knowledgeable can step in.
Cheers,
Andrew A.
Air War Publications -
www.airwarpublications.com/earticles