It seems to me that there are some missing Halachot in Tur/SA. For example, Hilchot Lashon Hara, WeHalchta Bidravaw, and Tamim Tihye. Feel free to add.
Sources aren't necessary.
Why are they missing?
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Tamim Tihye is in Yoreh Deah Siman 179 and the other Mitzvos and more are brought in Shulchan Aruch Horav (and other Achronim) in Siman 156. But I don't know why the Tur/SA doesn't mention them.