Disqualifiying a Divorce Bill where the Husband didn't fulfill a condition due to extenuating circumstances: Ketuvot 2b-3a
Case of Pishon the Camel Driver: Yevamot 107b
Allowing a woman to be divorced without a Bill of Divorce, in a circumstance where she should have needed a Bill Rabbinically: Yevamot 110a
Allowing a woman to be divorced with a Bill of Divorce which was lost at one point: Bava Metzia 19a
Allowing certain methods of signature on a Bill of Divorce, which are invalid for general bills: Gittin 19b
Requiring extra/less testimony by the deliverer of a Bill of Divorce on its validity, to prevent a challenge later: Gittin 3a [2x]
Allowing testimony by a single witness to allow a woman to re-marry, in certain cases: Niddah 8a