Three manuscripts of the Vitry Machzor are extant, the oldest of which, according to Abraham Berliner in his additions to Hurwitz's introduction to the Vitry Machzor (p. 172), is that in Reggio.
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On his father's side Isaac was a grandson of R. Simhah ben Samuel of Vitry, author of the Maḥzor Vitry; on his mother's side he was a nephew of Rabbeinu Tam, of Rashbam, and of Isaac ben Meir (RiBaM), a great-grandson of Rashi, and a relative of R. Eleazar of Worms.