On the site called "Elpenor," they show Psalm 13:3 of the Septuagint text like this:
3 πάντες ἐξέκλιναν, ἅμα ἠχρειώθησαν, οὐκ ἔστι ποιῶν χρηστότητα, οὐκ ἔστιν ἕως ἑνός*
But on the site called "The Orthodux Pages, they show this Septuagint Psalm thusly:
3 πάντες ἐξέκλιναν, ἅμα ἠχρειώθησαν, οὐκ ἔστι ποιῶν χρηστότητα, οὐκ ἔστιν ἕως ἑνός
[τάφος ἀνεῳγμένος ὁ λάρυγξ αὐτῶν, ταῖς γλώσσαις αὑτῶν ἐδολιοῦσαν· ἰὸς ἀσπίδων ὑπὸ τὰ χείλη αὐτῶν, ὧν τὸ στόμα ἀρᾶς καὶ πικρίας γέμει, ὀξεῖς οἱ πόδες αὐτῶν ἐκχέαι αἷμα, σύντριμμα καὶ ταλαιπωρία ἐν ταῖς ὁδοῖς αὐτῶν, καὶ ὁδὸν εἰρήνης οὐκ ἔγνωσαν· οὐκ ἔστι φόβος Θεοῦ ἀπέναντι τῶν ὀφθαλμῶν αὐτῶν.]
And they provide this English reading to go along with it:
3 They are all gone out of the way, they are together become good for nothing, there is none that does good, no not one.
Their throat is an open sepulchre; with their tongues they have used deceit; the poison of asps is under their lips: whose mouth is full of cursing and bitterness; their feet are swift to shed blood: destruction and misery are in their ways; and the way of peace they have not known: there is no fear of God before their eyes.
So, my question is, is there more than one "official" Septuagint, and if so, then how would one readily identify ... and communicate to others ... just which version of the Septuagint that one was referencing?
Addendum: From the NIV I've learned that the Masoretic Text tradition contains marginal notations that offer variant readings, which have sometimes been followed instead of the text itself. And, for the Psalms, the Juxta Hebraica of Jerome. Readings from these were occasionally followed where the Masoretic Text seemed doubtful. Might this, then, be a factor in why the Septuagint (or a particular "version" of the Septuagint) might differ from the Masoretic Text?