Bava Batra 105 - October 8, 6 Tishrei

If a seller says "I am selling you land the size of a beit kor measured out with a rope, more or less" - is the second part of the statement indicating a change of mind, or was it meant to keep open both possibilities? Ben Nanas says we hold by the last words. Rav points out that the rabbis disagree and hold that they split the difference since it is unclear what the seller intended. Why was it necessary for Rav to point this out when there is already a case in a Mishna regarding a rental agreement for "twelve months for twelve gold dinarim, one dinar per month" and Rabban Shimon ben Gamliel and Rabbi Yosi ruled in a case of a leap year that the rent for the thirteenth month was to be split between the owner and the renter? The Gemara distinguishes between the two cases, explaining why it may not have been clear that the law would be the same in both cases. Shmuel held that those who disagree and think that the language is unclear hold that the seller has the upper hand as the land is in the seller's possession (in a case of doubt, the burden of proof lies on the one trying to take something from the possession of another). When Shmuel pointed out that some disagreed with Ben Nanas, did he mean to say that he held like the others or not? The Gemara brings other similar cases to assess whether Shmuel held like/against Ben Nanas and after differentiating between the cases, concludes that Shmuel held like the rabbis. Rav Huna explains that Rav rules like Ben Nanas in a different, but similar case. Why was it necessary for him to teach that ruling, if Rav's ruling was known from a different case?