In several of the Tosafot lately (92-104) there is the expression "Amar li Rabbi." Do you know who is writing this and to whom is he referring?
In the margin of Tosfos on 90a, there appears a note that says, "[The Tosfos] from here until the end [of the Masechta] is copied from Tosfos Rabeinu Shimshon." We know that the rebbi of Rabeinu Shimshon was the RI.
Nonetheless, we find occasionally in Tosfos (such as on 107a, DH Mai) that Tosfos says, "It is perplexing to Rebbi... and Rabeinu Shimon explains...." This implies that it is not Rabeinu Shimshon who is writing, but rather his Talmid. Regarding this, A. A. Auerbach (Sefer Ba'alei ha'Tosfos) writes that part of the Tosfos in Kesuvos were worked on by Rabeinu Shimshon's Talmid, Rabeinu Eliezer mi'Tuch, and he is the one who added the words, "and Rabeinu Shimon explains" in some of the Tosfos.
M. Kornfeld