It appears a number of Christians are now interested in the recent translations of the Septuagint to English translations now available. I have recently looked at the Genesis genealogy account in one of them, the NETS and have found that there is an error which places the death of Methuselah as being 14 years after the Flood. The KJV shows him dying the year of the Flood. I am placing my calculations on here in pdf format to show the proof of what I am saying. We need to be careful with new translations.
Len McM
If you are right (and I did look at your calculations, though I didn't "proof" them), then the conclusion would seem to be that there is an error in the Septuagint itself, which is of course then carried over into the NETS English translation that you reference. This is likely the case if/since the same error is found in other English translations of the Septuagint.
Being aware that the Septuagint was a very loose translation, and by today's standards is not a good linguistic version of the original Hebrew, I am not really surprised by your finding.
What is interesting (and intriguing) is that Jesus Himself quoted from the Septuagint.
Maybe this shows that some of our nitpicky squabbles over translations are not as important as we like to think?!