1) Your question is asked by the Rosh: Since Rashi explains that in Rabah bar Rav Huna's story, they started eating before Shabbos and continued eating into Shabbos, why then does the Gemara bring a proof that in such a case it is sufficient to spread on a cloth, from a Beraisa which is referring to every

Shabbos, not specifically when they started eating before Shabbos?

The Rosh cites Rabeinu Yechiel from Paris who answers that the proof from the Beraisa is that just as even though one should not bring the table every Erev Shabbos before one makes Kidush, nevertheless if one did bring it first then it is satisfactory to spread a cloth and this is considered as if one never had brought the table, similarly if one was eating on Erev Shabbos and it became dark, then it is sufficient to spread a cloth and this is considered as if one has removed the table, and one can then make Kidush.

2) In fact according to the Rashbam the story about Rabah bar Rav Huna has nothing to do with Shmuel. See the Maharsha that the Rashbam is telling us that the text of the Gemara is not that the Beraisa supports Shmuel.

Instead according to the Rashbam, Rabah bar Rav Huna's story was not where they were eating after it got dark, but rather they came home from Shul and Rabah maintained that one should not bring the bread to the table before one has made Kidush. Even so, they did bring the bread before the Kidush, so what Rabah did was to spread on a cloth. Covering over the table is considered similar to removing it entirely, and therefore Rabah could now make Kidush.

This is what the Beraisa states: the table (i.e. the bread) should not be brought until Kidush has already been made but if it was brought prior to this, then one may spread a cloth and make Kidush. The Beraisa is therefore a proof for what Rabah did.

Chodesh Tov

Dovid Bloom