Study Guide Nazir 18

In the fourth attempt to answer Rabbi Ashi's question, we find a source explicitly stating that one who vowed to be a nazir while impure does not shave one's hair on the seventh day of purification. Rav Chisda attributes a braita we saw on a previous page a Mishna in Keritut 20b - one to Rebbi and one to Rabbi Yosi son of Rabbi Yehuda - regarding their debate about when a nazir who becomes impure begins their count of nezirut again - on the seventh day of purification or the eighth. What is the basis for their debate? From Rav Chisda's explanation of the Mishna in Keritut, is it possible to understand what he holds about whether the obligation of the sacrifice begins on the night of the eighth or in the morning?  A braita is quoted where two more opinions appear in connection with the dispute we saw between Rebbi and Rabbi Yosi bar Yehuda - from when do you start counting the days? Is it after the sin offering was brought or after the sin and the guilt offering? What is the basis for each opinion and how does each one deal with the verses that the other uses to prove his position?