Do you have anything regarding women covering that addresses the notion that it is only mentioned once and therefore cannot be anything of importance since prayer is mentioned several times by the Christ and the apostles spend a lot of time on the subject, but Jesus never says anything about it - just a letter to a certain group of Christians; therefore, it must be a local custom ...
It is a false restriction to say only what Jesus mentions is binding. Jesus said to the disciples (in red letters): "He who hears you hears Me, he who rejects you rejects Me, and he who rejects Me rejects Him who sent Me" (Luke 10:16). Thus, the words of the apostles carry equal weight as Christ's because they taught the words of Christ. As Paul pointed out:
"But I make known to you, brethren, that the gospel which was preached by me is not according to man. For I neither received it from man, nor was I taught it, but it came through the revelation of Jesus Christ" (Galatians 1:11-12).
"If anyone thinks himself to be a prophet or spiritual, let him acknowledge that the things which I write to you are the commandments of the Lord" (I Corinthians 14:37).
When someone tells me they believe a topic can be ignored because it is only mentioned once, I'm reminded of the teen who tells his exasperated mom, "But you only reminded me once. How was I susposed to remember?"
As far as we know, the law not to eat of the tree of the knowledge of good and evil was given only once, yet Adam and Eve were expected to follow it. To say that a law can be ignored because it is mention just once is folly. It is saying that God doesn't always means what He says. It is removing something from God's law, which God has stated is not to be done. "Whatever I command you, be careful to observe it; you shall not add to it nor take away from it" (Deuteronomy 12:32).
The claim is that what was taught in I Corinthians was only told to one group of Christians, but Paul says otherwise.
"For this reason I have sent to you Timothy, who is my beloved and faithful child in the Lord, and he will remind you of my ways which are in Christ, just as I teach everywhere in every church" (I Corinthians 4:17).
"But as God has distributed to each one, as the Lord has called each one, so let him walk. And so I ordain in all the churches" (I Corinthians 7:17).
"But if anyone seems to be contentious, we have no such custom, nor do the churches of God" (I Corinthians 11:16).
"For God is not the author of confusion but of peace, as in all the churches of the saints" (I Corinthians 14:33).
Paul did not tell one group of Christians to do one thing and others something different. His message was consistent. To conclude it was a local custom because it is written just once by Paul is a false conclusion. One might conclude it was local custom from their understanding of I Corinthians 11:16, a conclusion I would disagree with, but to do it from the number times mentioned, to whom it was mentioned, or by whom it was mentioned is not handling the Word of God accurately.