Yaasher koach. I especially liked the second part of the shiur.
On the issue of get, it seems to me that Tosafot is saying that a man who drafts a get with the intent that he might use it for either wife has da'at to use it for each. If brairah is not available to clarify that intent, retroactively, then the get for either wife cannot be deemed lishmah, because part of the husband's intent was potentially to use the get for his other wife. That would be very different than s'tama, where there is no invalidating intent.
Shalom L. Kohn
Thank you for your feedback!
As for your question: Tosfos is proposing that according to the Hava Amina of the Gemara, since the husband wants the option of using the Get for another woman, he does not truly intend to designate the Get for any particular woman at the time of the writing of the Get -- his verbalized intent for a specific woman notwithstanding. The Get is therefore considered to have been written Setama.
The question that one may ask on this is that we normally rule "Devarim she'b'Lev Einam Devarim." Even if the husband did have in mind to make the Get Setama, we should ignore his intention, since it is contradicted by what he says verbally! This may be why TOSFOS TUCH, in the Shitah Mekubetzes #11, writes that it is the scribe who makes the Get Setama - contrary to the request of the husband.
M. Kornfeld