Bava Batra 161A

מחק ⁠– פסול, ואף על פי שמקוים.

but a document with a reference to words written over an erasure is not valid, even if it is verified at the end of the document. At the end of a document, before the formula: Everything is confirmed and established, is written, any corrections made in the document are verified by adding to the text: On line so-and-so, such and such a word has been added, or some similar formulation. This may be done only for inserted corrections, not for erasures.

ולא אמרו מחק פסול ⁠– אלא במקום ״שריר וקיים״, וכשיעור ״שריר וקיים״.

The Talmud clarifies this statement: And they said that an erasure on a document renders the document not valid only if it is in a place on the document where the declaration: Everything is confirmed and established, should have been written, and only if the erasure is the measure of space in which the declaration: Everything is confirmed and established, can be written. The only concern with erasures is that the crucial formula: Everything is confirmed and established, might have been erased, as this would allow for unlimited forgery. If the erasure is such that this formula could not possibly have been erased, the document is valid.

ולרב ירמיה בר אבא, דאמר: אחורי הכתב ⁠– וכנגד הכתב מבחוץ; ליחוש דלמא כתיב מגואי מאי דבעי, ומחתים סהדי יתירי מאבראי, ואמר: אנא לרבות בעדים הוא דעבדי!

§ Rami bar Ḥama asked Rav Ḥisda: And according to Rav Yirmeya bar Abba, who says that the witnesses sign on the back of the written side, taking care that the signatures are exactly opposite the writing, on the outside let there be a concern that perhaps the party holding the document will write whatever he wants on the inside, i.e., the front of the document, adding to the text, and then have extra witnesses sign on the outside, and he will say to anyone questioning the number of witnesses being more than the minimum: I did this in order to increase the number of witnesses, the more to publicize the matters written in the document.