Verifying claims

Forgive the naive question but I’m not sure where to start …

I’m researching various incidents as subjects for possible pictures. One that interests me was on 5th June 1942 when pilots from 303 Squadron flying Vb Spitfires (or likely two Vb and one Vc) shot down three Fw 190s over the Channel near Le Havre. Or did they? It’s in the Ops Record – but the account is very garbled; some sources credit what would appear to be two of these kills to a different month; some just mention the one, that of Boleslaw “Mike” Gladych.

I’d also like to know about Count Czernin of No 17 Sqdn apparently knocking down THREE Bf 110s in the space of one minute on 25th August 1940: how would I ascertain which e/a they were?

Question is, how best to verify these or any other such events?

Thanks in anticipation.

Gary