Id like to ask why does the gemara assume that bimshoch hayovel is meyutar. Actually it is needed to prohibit the whole period between the luhot rishonot and shniot. As Rashi says, the pasuk gam hatzon vehabar was said only in the luhot shniot. It is true that we can learn the din of kol davar shebeminyan tzarich minyan acher lehatiro by the repetition in the luhot aharonot. But the pasuk is needed also to teach that it was prohibited to touch the mountain between luhot rishonit and shniot. So it not meduyak when the genara says "bimshoch havotel lama li"...?
Joseph Kayeri, Sao paulo, brazil
Rashi (5b DH Michdei) writes that we learn from "El Mul ha'Har ha'Hu" that as long as the mountain posseses Kedushah because the Shechinah is upon it, it is forbidden to touch it. Rashi writes that the Shechinah did not leave the mountain until the 20th of Iyar in the second year. So it is not the verse "Bimshoch ha'Yovel" that prohibits the period between the Luchos Rishonos and Luchos Sheniyos. It is the verse "El Mul ha'Har ha'Hu" that prohibits this.
I will just add, bs'd, that Tosfos (DH Michdei) disagrees with Rashi and writes that "Bimshoch ha'Yovel" implies that they were allowed to go back on the mountain on the very day of Matan Torah; they did not have to wait for almost a year, as Rashi says. Tosfos adds that since the only reason they were not allowed to ascend Har Sinai during Matan Torah was because of the Shechinah, it follows that as soon as the Shechinah went away, it was automatic that they were allowed once again to touch the mountain and there is no need to have a verse to tell us this. Tosfos concludes that "Bimshoch ha'Yovel" is extraneous and the only reason it is needed is in order to tell us that one needs another Minyan to permit anything forbidden in the first Minyan.
In short, according to Tosfos, "Bimshoch ha'Yovel" is not needed to prohibit the period between Luchos Rishonos and Luchos Sheniyos because going on the mountain was actually automatically permitted on the very day the Torah was given, once the Shechinah left.