Keritot, Chapter Six, Mishnah Four
Since yesterdays mishnah dealt with Yom Kippur, todays mishnah deals with the effect that Yom Kippur can have on those who are liable to bring expiatory sacrifices.
1) Those that are liable to hatats or to certain ashams and Yom Kippur passes over them, are still liable to bring them after Yom Kippur.
2) Those that are liable to asham taluis are exempt.
3) He who has committed a doubtful sin on Yom Kippur, even at twilight, is exempt, because the whole of the day effects atonement.
Section one: Yom Kippur does not atone for sins if he finds out before Yom Kippur that he certainly sinned. Thus if one becomes liable to bring a hatat or a certain asham before Yom Kippur, he is still liable after Yom Kippur.
Section two: However, if he has doubtfully sinned and needs to bring an asham talui, Yom Kippur atones and he need not bring the asham talui after Yom Kippur.
Section three: Yom Kippur atones for doubtful sins even if they are committed (unwittingly) on Yom Kippur itself, and even at the very end of the day. It is actually hard to imagine this happening unless one simply miscalculates the date of Yom Kippur and eats meat which might or might not have been forbidden fat. For if one knows that it is Yom Kippur, he shouldnt have been eating in the first place.