> (wonder why you didn't choose to quote this sentence as well, hmmm: "Yet the historical, demographic, and geographical evidence does not support this entirely logical and neat story line—a fact to which Weinreich himself gives evidence in his notes.")

Because that sentence is from a separate part of the article and refers to an entirely different point. I'll outline the structure for you:

> Weinreich’s first innovation in the History was to argue, against apparent common sense and abundant personal experience, that Yiddish was formed not through isolation but through constant interaction combined with a chosen separateness.

> Archeology supports this part of Weinreich’s argument.

> Weinreich’s second argument is equally counterintuitive. Though in some places Yiddish and German were mutually understandable, he assiduously argued that they are different languages. But Weinreich deployed his formidable linguistic artillery to argue, contrariwise, that despite significant variations in spoken and written Yiddish across the expanse of Europe (western Yiddish, more purely German; eastern Yiddish, heavily Slavic; southern Yiddish, with influence from Hungary and the Balkans), Yiddish forms one language and shares one cultural sphere and worldview, quite distinct from the surrounding culture. In short, Yiddish and German are different, but all Yiddish is one.

> Once he demonstrated that Yiddish is an independent language, Weinreich explained how it came to be, first as an altered language formed among medieval Jewish trading settlements in the French–German borderland along the Rhine valley. Weinreich deduced from traces left in early Yiddish that these first Jewish immigrants to the heart of Europe spoke a Romance language, having left Hebrew, Aramaic, and Greek behind when they left the eastern Mediterranean, although Hebrew and Aramaic were still languages of study. But early on (in the 10th or 11th century) these Jews from Rhineland France, presumably through contact with Jewish settlements in southern Germany, converted from old Judeo-French to western Yiddish, which was more purely German with some elements of Latin or early French. In subsequent centuries—when, exactly, is a source of considerable debate—this language moved east with Jewish emigrants, settlers, and refugees, either in the 12th century (after the Crusades and persecutions) or in the 14th or 15th. There it picked up a significant cargo of Slavic vocabulary and expressions and became the Yiddish more familiar today: eastern Yiddish.

> Yet the historical, demographic, and geographical evidence does not support this entirely logical and neat story line—a fact to which Weinreich himself gives evidence in his notes. Yiddish blossomed in printed books from the 16th century onward, but Weinreich argues that Yiddish began in the 10th century in the Rhineland—though there are little more than a dozen extant texts in Yiddish from before 1400. Many of these early traces of Yiddish are only a few lines long and, aside from the marginal glosses of the Talmudic scholar Rashi (c. 1100) from the Champagne region, the early texts do not congregate in the “right” geographic area.

The claim that the historical evidence does not support the idea that Yiddish originated in tenth-century France is quite different from the claim that the historical evidence does not support the idea that segregation was a privilege given to eleventh-century Jews at their own request. You want the sentence you quoted to mean the latter of those, but an honest reader would have to admit that it means the former.