The cited verse above, from the KJV, reads: “And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the Lord.” This verse seems to have been corrupted even before the Septuagint!
I will cite some of the oldest manuscripts we have access to in an attempt to restore the original meanings to some current errors. An important witness is the Hexapla, and I will cite the 1881, 15-volume Library of Universal Knowledge, vol. 7, p. 514:
“HEXAPLA (Gr. hexapla, ‘the sixfold’), a celebrated edition of the Septuagint version, compiled by Origen for the purpose of restoring the purity of its text, and bringing it into closer agreement with the original Hebrew. Owing to the multiplication of transcripts of the Greek text, numerous errors had crept in; and in the frequent controversies which arose between the [Judaeans] and the Greek or Hellenist (q.v.) Christians, the latter, in appealing to the Greek text, were often mortified by the discovery that it by no means represented faithfully the Hebrew original. In order to meet this evil, Origen undertook to provide a means of at least verifying the genuine Greek text, as well as of confronting it with the original. With this view he prepared what is known as his Tetrapla, or ‘fourfold’ version, which he afterwards extended into the hexapla. The Tetrapla contained, in four parallel columns, the Septuagint version, together with those of Aquila, Symmachus, and Theodotion. The hexapla contained, in addition, the Hebrew text, together with a transcript of that text in Greek characters. In some parts of the Old Testament there were superadded one, two, and even three other versions; so that in some parts the work contains nine columns, whence it is occasionally designated the Heneapla, or ‘ninefold.’ Of the origin of these latter versions little is known.
“The hexapla, however, was something more than a mere compilation of these versions. In the margin were given notes, chiefly explanatory, as, for instance, of the Hebrew names. But a still more important characteristic of the work were its restorations and corrections of the original, in which Origen was guided chiefly by the version of Theodotion. This, however, he did not effect by arbitrary alterations of the received text; but, while he retained the common text, by indicating with the help of certain signs (an asterisk for an addition, an obelisk for a retrenchment), the corrections which he sought to introduce. Both these texts, the common (koiné ekdosis)and that of the hexapla, are found combined in existing MSS. The hexapla, as a whole, has long been lost; several editions of those fragments of it which it has been possible to recover have been printed; by far the most complete of which is that of the celebrated Benedictine, Montfaucon (2 vols. fol., Paris, 1714), which retains, so far as it was preserved in the MSS., the arrangement and even the asterisks and obelisks of Origen. For a more detailed account, see the preface and Præliminaria of this learned work.” (Incidentally, these two large volumes are in PDF, and can be downloaded from my website: Volume 1, Volume 2)