Caspar René Gregory published a cataloging system for the Greek New Testament manuscripts in 1908. In 1963, Kurt Aland expanded Gregory's work, and the Gregory-Aland (GA) numbers became the industry standard for referencing Greek New Testament manuscripts.
We must face the reality that while the original 39 OT manuscripts and 27 NT manuscripts were inspired by God [Lit. “God-breathed”] (1 Tim. 3:16), as the authors were moved along by the Holy Spirit (1 Peter 1:21), this was not the case with the copyists thereafter. Yes, hundreds of thousands of scribal errors crept into our manuscripts.