Reference for Ketubot 164:6

מהו דתימא התם הוא דלא כתב לה דקנאי ודקנינא אבל הכא דכתב לה דקנאי ודקנינא אימא סמכה דעתה קמ"ל:

What might you have said? [That the restriction mentioned applies only] in the former case because the levir does not write [in the ketubah] “That which I acquired and that which I will acquire,” but here, where he does write, ‘That which I acquired and that which I will acquire,” she relies upon this guarantee, hence it needed to teach us this in both cases.

Jastrow