I was talking with a rabbi, who mentioned that once he had seen a list of discussions in the Talmud (most probably authored by R' Eliashiv), that were in an unexpected place, and by learning only the relevant tractate of Talmud, one would easily overlook them. I could remember one such example mentioned here, namely on Arakhin 3b an important issue is discussed about sukkot in spite of having its own tractate. So I am looking for halakhically relevant sugyot not present in their own tractate. Have you seen this list? Or can we come up with such a list in a community wiki format?
This isn't a direct answer, but it is useful relevant information. There is a book called Sefer Hamafteach that is an index of the entire talmud. So for example if you wanted to see all sugyot related to Sukkah, you could look up the entry and find those that aren't in the expected Masechet. There is both a hebrew and english edition.