Did Cyprian of Carthage Know About the Johannine Comma?

I will provide a couple of quotes from R.E. Brown and encourage you to consult his work (The Anchor Bible Commentary on the Johannine Epistles, Appendix IV, pages 775-787).

"Within the uncontaminated Greek tradition the Comma is never quoted by a Greek author of the first Christian millennium. This silence cannot be dismissed as accidental; for the Greek text of 1 John 5:7 is quoted (e.g., three times by Cyril of Alexandria) without the Comma. And there is no reference to the Comma by the Greeks even in the midst of the trinitarian debates when it should have been of help were it known" (page 777).

He also writes that Cyprian's citation "and these three are one," is undoubtedly taken from the Old Latin text of 1 John 5:8 and refers to the spirit, the water, and the blood. Brown notes that Cyprian's application of 1 John 5:8 from the Vetus Latina to the Father, Son, and Holy Spirit "need not represent a knowledge of the Comma" (Brown 784). Even if Cyprian was citing the Comma, it still does not prove that the Comma was ever in any early Greek text.