What does the Pasuk mean when it says "v'Nod'ah ha'Chatas"? Obviously they will not bring a Korban before it is known!
Ramban #1, Moshav Zekenim #1: It is a manner of speech, as if to say 'When they know that they have sinned... '. 1
Ramban #2, Moshav Zekenim #2: To teach us that they are only Chayav if they know for sure that they have sinned - but not on a Safek. 2
Ramban #3 (Toras Kohanim): To teach us that, not only must they know that they ruled incorrectly, but also exactly what their mistake was. 3