I’m sure that there was an original Septuagint. It seems highly unlikely that there were parallel Septuagints created at the same time. But like the books of Scripture, they were copied with either inadvertant or deliberate changes over time.
More likely, however; that the "Legend of the 70" Septuagint is just that - - - a Legend!
For the fun of it I thought I'd provide a decidedly "anti" Septuagint link for your edification.
Then, for a fair and balanced presentation, an article from an approved Catholic source.
"lastly, the very language of the Septuagint Version betrays in places a rather imperfect knowledge both of Hebrew and of the topography of Palestine, and corresponds more closely with the vulgar idiom of Alexandria."
Catholic Encyclopedia - The Septuagint