What exactly is the court notarizing? TB Ketubot 21

What is good analogy for kiyum shtarot (קיום שטרות) certifying the authenticity of the document? The court is notarizing the document. But what is the court actually notarizing? Rabbi Yehuda Hanasi and the Sages disagree what the court is notarizing. The discussion begins at the very bottom of TB Ketubot 20b and continues on today’s daf TB Ketubot 21.

“MISHNA: If this witness whose name is signed on a document says: This is my handwriting and this is the handwriting of my fellow witness, and that witness says: This is my handwriting and that is the handwriting of my fellow witness, these witnesses are deemed credible and the document is ratified, as together they provide testimony authenticating both signatures. If this witness says: This is my handwriting, and that witness says: This is my handwriting, and neither testifies with regard to the signature of the other, they must add another witness with them who will authenticate the signatures of the two witnesses, as otherwise, each of the witnesses would be testifying with regard to half the sum in the document; this is the statement of Rabbi Yehuda HaNasi. And the Rabbis say: They need not add another witness with them. Rather, a person is deemed credible to say: This is my handwriting. The testimony of the two signatories about their own signatures is sufficient.”

“GEMARA: The Gemara says: When you analyze the reasoning for the opinions of the tanna’im, say that according to the statement of Rabbi Yehuda HaNasi, the witnesses are testifying about their handwriting and authenticating their own signatures. Therefore, if each witness testifies only with regard to his own handwriting, there is only one witness authenticating each signature. According to the Rabbis, the witnesses are testifying about the sum of one hundred dinars that is in the document and are not authenticating the signatures at all. Therefore, the testimony of the two witnesses who signed the document is sufficient to ratify the document.” (Sefaria.org translation)

Rabbi Yehuda HaNasi’s says the court is notarizing the signatures and not the content of the document. In other words, the court is acting like our modern public notary. The person notarizing the document doesn’t need to know what’s contained therein. A person signs his signature in front of public notary and he notarizes it. Since the court is certifying the signatures two witnesses are required. In the first case in the Mishna there are two witnesses testifying to the validity of each signature. In the second case only one witness is testifying on a signature. Rabbi Yehuda HaNasi holds though one witness can double dip and authenticate his own signature and the other signature on the document as long as a third witness authenticates as well.

The Sages holds the position that the court is notarizing the content of the document. The document has already been signed by two witnesses. As long as those two witnesses come before the court and testify the signatures are theirs that is sufficient to notarize the document. However, if the court is using other means of certifying the document, then the Sages would agree with Rabbi Yehuda Hanasi that two witnesses are required to authenticate the document.