(This question is also asked here on history.SE for a different perspective.)
Considering that variations have occurred in the Torah's text over time (I think the Gemara may mention events where a few scrolls were found and they averaged out the differences for a new scroll?), and there is a Gemara that says what the middle letter of the Torah is but it's off by a few hundred letters (and that Gemara says we are not expert on the missing and added letters), and when you see a quote of a possuk in the Talmud you often see spelling differences from what the actual Torah has (mainly in terms of the letter vav), and the Septuagent has differences from our text, and the Dead Sea Scrolls has differences from our text, and so on. Now, I know that the Yeminite and Sfardic and Ashkenazic Torahs are remarkably similar, but I do not know at what point they were the same before the differences occurred. So when was the manuscript from which all Jews of the world standardized the Torah? I heard it was sometime around 1000 CE but I can't remember the source.