Ketubot 89 - How to collect divorce settlement
Imagine that a woman comes to court and presents a Get with which her husband divorced her. Then she wants him to pay the amount of the Ketubah. However, she does not have the Ketubah document itself, claiming that it was lost. Normally, she should not be able to collect: anybody who wants to collect a payment should present a loan document (in this case it is the Ketubah). If it is lost, his money is lost.
However, here - since the Ketubah is the enactment of the court - it has the same power as though the document was actually present, and so she can collect the money. Her former husband's claim that he paid the Ketubah is not believed. If he did, they should have torn the Get, given him her Ketubah or the payment receipt.
Now consider the next case: the woman comes with the Ketubah, but without a Get. She wants the payment, but the husband claims that based on the rule above she already collected her payment with her Get, claiming that the Ketubah was lost, and now she has put away the Get, and produced the Ketubah. As for his receipt, he says he lost it. In this case, the husband wins, because she does not have a Get, and indeed could be collecting the money twice.
Rabban Gamliel adds that in the "time of danger" people were afraid to keep their Get or Ketubah, because the idolater were persecuting for the performance of commandments. From this time on, a woman is able to collect her payment even without the Get, because she may have destroyed it right after being divorced.
Art: A group portrait of a husband, wife and their child by Francis Alleyne