The Septuagint in a few papyri? What about the witness of Codex B, Sinaiticus and Alexandrinus? Origen must have been working with some pre-existing text when he was making his corruptions.

Whether there is no extant BC dated manuscript does not make the existence of a BC Septuagint a lie.

For many years the Reformers did not have BC dated Hebrew texts. It was only in the 1940s when the Dead Sea Scrolls were discovered that we had actual physical evidence supporting the pre-Christian existence of the Mesoretic Text.

Or again, the KJB says there are unicorns, and yet not one live or dead specimen is known to exist.

It is Reformation tradition that informs us there was a LXX, despite the ancient fabrications. This view is still held to by various reputable King James Bible defenders and supporters.

Moreover, the traditional view does best fit the Bible facts:

These were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so. Therefore many of them believed; also of honourable women which were Greeks, and of men, not a few. (Acts 17:11, 12).

Note that these verses show that it was also Greeks who were searching the Scriptures. How could those Gentile converts search the Hebrew? Obviously they were searching the Greek common translation, namely, the Septuagint.

"And when the Gentiles heard this, they were glad, and glorified the word of the Lord: and as many as were ordained to eternal life believed. And the word of the Lord was published throughout all the region." (Acts 13:48, 49).

This would indicate that the Septuagint was being used and called "the word".