This is obvious, they used other English Translations. They could not be KJV only, they were KJV Finally.
Which version of the KJV is the final and perfect one?
Based on what the KJV translators say in their Preface, it doesn't make any sense that they were KJV finally. For example they stated the necessity of
translations (plural) into a language the common people could understand. The KJV may have served its purpose, but it's out of date.
I've actually heard people say that the form of English used in the KJV is the most perfect and pure form of English that ever was and will ever be; and for this reason the KJV is the most perfect translation that is and shall ever be. To that the KJV translators would roll over in their graves. Maybe the KJV language is a perfect and pure form of the English language, I don't know. But regardless, as far as the Bible is concerned, if people can't understand it it's useless.
The NKJV is an improvement, but is it the final one? Or the 1611, the 1629, the 1638, the 1762, or the 1769?
"But how shall men meditate in that, which they cannot understand? How shall they understand that which is kept close in an unknown tongue? as it is written, Except I know the power of the voice, I shall be to him that speaketh, a Barbarian, and he that speaketh, shall be a Barbarian to me. [1 Cor 14] The Apostle excepteth no tongue; not Hebrew the ancientest, not Greek the most copious, not Latin the finest. Nature taught a natural man to confess, that all of us in those tongues which we do not understand, are plainly deaf; we may turn the deaf ear unto them. The Scythian counted the Athenian, whom he did not understand, barbarous; so the Roman did the Syrian, and the Jew (even S. Jerome himself calleth the Hebrew tongue barbarous, belike because it was strange to so many) so the Emperor of Constantinople calleth the Latin tongue, barbarous, though Pope Nicolas do storm at it: so the Jews long before Christ called all other nations, Lognazim, which is little better than barbarous. Therefore as one complaineth, that always in the Senate of Rome, there was one or other that called for an interpreter: so lest the Church be driven to the like exigent, it is necessary to have translations in a readiness. Translation it is that openeth the window, to let in the light; that breaketh the shell, that we may eat the kernel; that putteth aside the curtain, that we may look into the most Holy place; that removeth the cover of the well, that we may come by the water, even as Jacob rolled away the stone from the mouth of the well, by which means the flocks of Laban were watered [Gen 29:10]. Indeed without translation into the vulgar tongue, the unlearned are but like children at Jacob's well (which was deep) [John 4:11] without a bucket or something to draw with; or as that person mentioned by Isaiah, to whom when a sealed book was delivered, with this motion, Read this, I pray thee, he was fain to make this answer, I cannot, for it is sealed. [Isa 29:11]"