One should note that the last two editions of Nestle-Aland include the word in the text.
This got me to thinking back to the way the NA changed "Word of God" to "Word of the Lord" in several places, so I did some digging.
The conclusion that I came to is exactly what has been stated here that there are three offices that can be fulfilled by one person or by multiple people.
The pastor is
an elder. He's answerable to the elders, but he's the leader. He's ultimately answerable to God.
By being anserable to them, they can remove him. If they are godly, it will be because he's doing something wrong. However, it could also be for wrong reasons, such as fear of running off the big contributors.
The overseer is
an elder as well. Since the etymology of the word comes from the idea of one who oversees the business or money of what he's the overseer of, I think it applies to that.
The pastor, or another elder can be the overseer. However, in order to remove himself from even the appearance of the possibility of malfeasance, I think this authority should be an elder other than the pastor.
Elder is a position that can be held by one or by many within a congregation. There can be one person who is
the pastor/elder/overseer, or there can be many.
However, a church (little "c") is not a democracy. It's run by the elders who are appointed. How are they appointed? There are several possibilities.
An elder can shepherd (verb) without being
the shepherd of the congregation, just as when the word is used to shepherds of physical sheep. They can oversee the congregation without being
the overseer. Just as there are different bosses at a job. Your boss may not be
the boss.
Government has the same idea, but more coequal. There is one leader who is the leader and can make decisions, but he's answerable to the others.