So let me try to explain to you again, even though you might get a better explanation from actual OT-scholars such as the guys from the IOSCS (
http://ccat.sas.upenn.edu/ioscs/):
The Septuagint is just a Greek translation of the Old Testament that was mostly made between 250 BC and 100 BC. So Papyrus Rylands 458 does indeed give you (some) text of Deuteronomy, but in the Septuagint’s translation.
What makes the Septuagint the Septuagint and different from other Greek translations that were around is the text-family that the Septuagint translations are apparently based on:
Back in the days when the OT got translated into Greek there was not just one version of Deuteronomy etc. around, but many – probably a bad example, but a bit like there’s an Alexandrian text-type for the Greek NT and a Byzantine text-type.
Back in the renaissance it was thought that the Septuagint was just a rather shoddy translation of the original Hebrew text, which was thought to be best preserved in the Masoretic Text. These days – with new findings from Qumran etc. – OT-scholars assume that the Septuagint may well be based on texts that are even older than the Proto-Masoretic text that we no longer have.
There is no one original Septuagint that somehow survived in the desert sand, but we have many textual witnesses to it, from which the texts of the Septuagint can be reconstructed, just like the original texts of the New Testament can reconstructed by comparing their many textual witnesses. And no, not that it matters, but whilst being the oldest we have the Papyrus Rylands 458 is not the only one of the Septuagint that dates before the NT:
https://en.wikipedia.org/wiki/Septuagint_manuscripts
https://en.wikipedia.org/wiki/Septuagint#Printed_editions
https://en.wikipedia.org/wiki/Textual_criticism
Of course there must have been many more copies of the Septuaginta around in NT times, but you see: that’s quite a while ago. A long time in which libraries got sacked and burned and in which Papyri just rots if not kept under perfect conditions. The same holds true for the entire Bible: most early manuscripts for both the Old and the New Testament are lost. So if you don’t deem sources like the Codex Sinaiticus (that already contains copies of copies of copies …) trustworthy, you might as well chuck your KJV out of the window, because it is based on even later manuscripts than the Codex Sinaiticus.
Now: The NT is written in Greek. Its authors don’t need to tell us that they (not Jesus, who spoke Aramaic and who did not write the NT) quote from the Septuagint when quoting from the Old Testament. All we need to do is to compare their quotations of the Old Testament with the Septuagint’s textual witnesses and we’ll find that they use the same wording. Slight variations here and there can be explained by the New Testament authors quoting the Septuagint texts from memory.
Again: I don’t quite see why you find it problematic that the NT authors quoted the OT in Septuagint translation. Is it possible that you just had a knee-jerk reaction to something kerwin said and now find it difficult to admit that you were wrong? Don’t worry! It’s ok to get things wrong here and there, happens to all of us occasionally.