[Franek Grabowski]

I think that there is a gross misunderstanding of the topic.
The issue discussed is not claims but verified and credited victories. There were various systems of verification and approval of victories in different countries and they often differed significantly. One should not blame pilots of deficiencies of those systems.
In general the RAF system was quite liberal up until late 1942-1943, when a more thorough verification was introduced.Up to this time, there were several inconsistencies in the system, and apart of crediting shared victories as individual ones, claimed victories were often upgraded and not downgraded.
Germans created their own system, reputedly very rigid, but actually quite inefficient. The general problem is a gap in a paperwork. Endless discussions concern lists of victories, but those are not sufficient to match victories with actual losses. This is quite apparent during the Battle of Britain, where in most cases it is not possible to match combatants with any certainty. RAF suffered losses to technical reasons, bad weather and blue on blue or friendly fire, and this was not insignificant. The situation continued through 1941 and 1942 and a general comparison of RAF losses and German victories do not tell the truth about those combats.
For example, during Circus 68 on 9 August 1941, JG 26 was credited with 6 victories against 5 actually lost. Looks fine, despite discrepancy which still should not happen to the German system. Nonetheless, according to the research of Andy Saunders, three of the lost Spitfires fell dwon due to friendly fire incidents. So, for the 6 victories there are only 2 losses, and out of those only loss of P/O Casson can be matched to the victory of Hptm. Schopfel.
Therefore a through scrutiny should be made before drawing a general conclusions, though I guess it would never be done because of volume of documents that would need to be reviewed.
Aside, there is a bit of rivalry concerning JG 2 and JG 26 amongst the researchers. I have to note that the essential problem is, that both JG 2 and JG 26 were a subject of the same rigid German victory crediting system. So how it could be the system awarded more false victories to JG 2 and not to JG 26?