The Lufwaffe had quite precise system of confirmation of victories. Using this, numbers are very trusthworhy. Btw., there were many people searching about this all the years after WW2, of course using comparation with known loses on other side. And if these numbers are not true, there should be many books about it, am I wrong? Sometimes there are exceptions, of course, i.e. recently I have read something about Hans Joachim Marseille, something like he was able to shoot down more aircraft, then were in air in that time...
On the other side, if you take reports of gunners of USAAF 8. Army, after about two of their airraids to germany there can be no Luftwaffe, because of it had all fighters shooted down by brave gunners...