I Corinthians 1:2
"To the Church of God that is in Corinth; to those who are sanctified in Christ Jesus, called to be saints, together with all those who in every place call on the Name of our Lord Jesus Christ, both their Lord and ours."
St Paul is stating that all those who are called to be saints and are sanctified in the Lord are members of the Church.
I Corinthians 12:13
"For in the one Spirit we were all baptized into one body"
This is typical of St Paul. Throughout his epistles, he emphasizes that those who are baptized and are being sanctified are part of the Body of Christ, which is his Church. So long as they have the Holy Spirit and a functioning community of leaders, teachers, healers etc., they are a valid church.
Well, yes, kinda. What's typical of St. Paul is that he writes circuitously, from presuppositions, rather than providing definitions like a catechism.
Just a peripheral issue to this article, anyway. As a former Tulsa resident, I wish this congregation the best, wherever they're going.