The gemara attacks R. Yochanan's position that neither a change in wine or a change in place requires a new bracha. The gemara asks, but didn't we previously refute R. Yochanan's position (101b)? The gemara answers, this is another refutation.
Rashbam (Neima) states that the reason for the second refutation is so that if someone were to answer the first refutation or discredit the source upon which the first refutation is built, the second refutation will be in place.
This seems to open up a world of possibilities. Rashbam is interpreting the gemera's (Ravina/Rav Ashi) answer. In other words, the final editors of the gemara included a second refutation because they were concerned that a the first refutation would fall in POST Talmudic times. Specifically, an answer or a discredtation of the source used in the Talmud's times. Further, the concern seems to be to be sure that R. Yochanan's position is not followed Halacha L'Maaseh. In other words, were it not for the second refutation and the first refutation were answered or discredited, R. Yochanan would be a viable shita.
On a contemporary basis, isn't this significant? 1) Does it open up the concept that the editors of the gemara did not intend that the acceptance/rejection of positions was not intend to end with the completion of the gemara? 2) In certain cases, don't we have better critical source that in the times of the gemara? Or, more generically, in certain cases, aren't we better informed about the 'facts' than in the times of the gemara?
Is this too much of a stretch?
The Rashbam is not saying that they were concerned that the first refutation would fall in " post Talmudic times." The Rashbam is not explaining why the compilers of the Gemara included the second refutation in the Gemara. Rather, he is explaining why the Amora'im themselves bothered to ask another question on Rebbi Yochanan's opinion, when their first question already refuted it. The Rashbam answers (based on the text of the Gemara here) that in their own times, the Amora'im gave another refutation, in case another Amora would come in their times and answer the first one.
We find in many places that an Amora is not able to argue with a Tana. If an Amora makes a statement and a contrary statement is found in a Beraisa or other Tanaitic source, then the Amora's statement is refuted (except for certain Amora'im, such as Rav, who had the status of a Tana, Kesuvos 8a). Similarly, it is recorded in many places that a Ga'on (who lived after the times of the Amora'im) does not have authority to argue with an Amora. Only when there was already a dispute among the Amora'im on the matter and the matter was never solved, then the Ga'on may issue a ruling based on what he sees to be the more logical opinion. (See Beitzah 11a, for example.)
The rule that we follow the opinion of the "Basra'a" (the "later" or most recent authority) applies only to authorities in the same categorical generation (such as Amora'im). If a modern-day authority wants to argue with Abaye, the Halachah does not follow the modern rabbi's opinion due to his being a more recent authority. The Rosh writes that even in the times of the Amora'im, the Halachah follows a Basra'a only up to the times of Rava, but not the later Amora'im.
Be well, Mordecai