1,813. When the Ex-Husband Has the Get
Hilchos Geirushin 10:10
The Sages required that the sister of the woman betrothed by the man (in halacha 10:8) be given a get so that people shouldn’t think that the first woman was betrothed only conditionally, which would enable the man to marry her sister. Since the sister was given a get, the first woman is prohibited to him so that people shouldn’t think that he married his ex-wife’s sister.
Hilchos Geirushin 10:11
Let’s say that a scribe wrote a get but he made a mistake and gave the get to the man and the receipt for paying the kesubah to the woman, or the couple made a mistake and the man took the get and the woman took the receipt, and they mistakenly thought that divorce was effected. Later, the get is found to be in the man’s possession. If the woman hasn’t already remarried, she is considered not to have been divorced. The man should give her the get in front of witnesses, at which point divorce is effected. However, if the woman has already remarried and her first husband later shows up with a get saying that she wasn’t divorced because it never reached her, then we don’t accept his words and the woman is not prohibited to the second man. Rather, we assume that she was divorced and she lost the get, which the first husband found and now wants to use to make her prohibited to her new husband.