1)
What is "u'Netziv Echad Asher ba'Aretz" (after listing the 12 Netzivim)?
1.
Sanhedrin 12a #1: One of them was appointed over all of them. Rashi - this was Azaryah, like it says in verse 5.
2.
Rashi citing Sanhedrin 12a #2: The extra one was for Chodesh ha'Ibur. 1
1
All agree that Azaryahu was appointed over all of them, like it says in Melachim I, 4:5. They argue about whether "u'Netziz Echad" refers to him, or to someone else. (PF)