The problem of overclaiming is very popular. In my last material about A/A defence of Warsaw in 1939
I have made deep an analys of overclaiming rate by Polish fighters and polish A/A defence in IX 39. It is very have rate, for example Polish A/A defence had claimed 97 shot down German planes and in fact there were destroyed at least 8 (8 confirmed in German documents). So, it is 12-rate overcaliming!
If we considern overclaiming rate among pilots of Brygada Pościgowa (PZL P11 P.7a), we wold get smaller figure: 43 claimed as destroyed, 9 probablers and 20 damaged. There were in fact 17-20 total destoryed Lw plases "over Warsaw' 1-6 09.39 (damage >60%).
Regards,
mw
See the cover
http://zbiam.pl/wojsko-i-technika-historia-12015/