Gittin 82A

דקא מדלג ותני חד חד; שמע מינה.

as it teaches by skipping one by one. The examples given relate to one witness missing, e.g., 7 ties and 6 witnesses, and so on. They do not include a case in which two witnesses are missing, e.g., 7 ties and 5 witnesses. This indicates that the dispute between R' Akiva and Ben Azzai is only with regard to the signature of one witness. The Talmud affirms: Conclude from it that this is so.

אמר אביי: שמע מינה, האי קרוב חתים אי בעי ⁠– בין בתחילה, בין באמצע, בין בסוף.

Abaye said: Learn from it that this relative, who is allowed to sign a folded and tied bill of divorce, can sign if he wants to sign, either at the beginning, as the first signature, in the middle, or at the end.

ממאי ⁠– מדלא קבע ליה מקום. ושמע מינה: מכל תלתא מקיימינן, ולא בעינן רצופין.

From where does Abaye infer this? From the fact that it did not designate a place for him to sign. And learn from it, as well, that from any 3 of the witnesses who signed on a folded and tied bill of divorce, we can ratify the bill of divorce, i.e., it can be ratified based on their signatures. And we do not need to confirm the signatures specifically of 3 consecutive witnesses.

דאי סלקא דעתך בעינן רצופין, לקבע ליה מקום להאי קרוב ⁠– בתחילה או באמצע או בסוף; ולכשר ביה טובא.

As if it enters your mind that we need consecutive witnesses, then they should designate a place for this relative to sign, in the beginning, or in the middle, or at the end, and they should then validate the use of many disqualified witnesses. It could have been instituted that every third witness may be disqualified. Since in any group of 3 witnesses, two of them would be valid, more than one disqualified witness could be allowed. Since it is possible to ratify a bill of divorce by confirming signatures that are not consecutive, and therefore there is concern that the court will rely on two disqualified witnesses, the rabbis consequently allowed the use of only one disqualified witness.