Whilst I cannot confirm or deny your statement (I don't know Greek), I do know there is evidence outside of Codxes alone.
Nick Sayer's lists Tertullian, Beatus of Liébana, and the Book of Armagh. In all honesty, I find this to be underwhelming, but I think we should also consider the critical text. This is a minority reading in the Textus Receptus. If we are going to claim the KJV/TR are in error here, then at least be consistent and say that the critical text is wrong for having hundreds more minority readings than the TR.
Additionally, consider the context and how the TR and CT contrast.
Revelation 1:8-11
(KJV) "I am
Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty. I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ. I was in the Spirit on the Lord's day, and heard behind me a great voice, as of a trumpet, saying, I am
Alpha and Omega, the first and the last: and, What thou seest, write in a book..."
(ESV) "'I am the
Alpha and the Omega,' says the Lord God, 'who is and who was and who is to come, the Almighty.' I, John, your brother and partner in the tribulation and the kingdom and the patient endurance that are in Jesus, was on the island called Patmos on account of the word of God and the testimony of Jesus. I was in the Spirit on the Lord’s day, and I heard behind me a loud voice like a trumpet saying, 'Write what you see in a book...”
Notice how the TR in verse 8 has the Lord talking, then in verse 11, it reconnects to verse 8, applying it to Christ. But when you look at the CT, the phrase "Alpha and Omega" is removed from verse 11, disconnecting it from Christ in the direct context.
That seems like a doctrinal change. As Thomas Ross states:
"The Received Text identifies Christ, the speaker in 1:8, 11, as the Almighty, the Alpha and the Omega, the beginning and the ending, the first and the last. The critical text, by adding the word 'God' in v. 8 and omitting the phrases highlighted above in v. 8 and v. 11, change the speaker in v. 8 from Christ to the Father, and remove the testimony to Christ’s Deity from this passage."
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