Ketubot 21: Witnesses, Judges, and Stumped Amoraim

Starting with the mishnah on the bottom of the previous daf - the case of witnesses who testify to their own handwriting and also to that if the co-witness - that's credible and upholds the document. But what if they only speak to their own handwriting, and not the other guy? It's a machloket whether the authentication of the other guy, beyond his own corroboration, is necessary. Also, can a witness become a judge? Does a judge need to have been able to be a witness? The discussion begins with the witnesses for the new moon. There are open questions here, specifically whether a judge can be a witness for non-Rosh Chodesh cases (like documents) and a hierarchy of each rabbi asking up, to the next one with greater knowledge.