Resources for medieval musicology and liturgy
Kenneth Levy already studied the sources of Beneventan and Ravenna chant concerning the Vigil Mass for Holy Saturday which was connected with the Tractus "Sicut cervus desiderat". A very unique version has been transmitted by the Benedictional roll of Bari.
The illuminations make it evident that baptism was connected with this celebration of the cathedral rite.
Levy, Kenneth. 1970. "The Italian Neophytes’ Chants". JAMS 23: 181-227.
The Sicut cervus is certainly part of the Beneventan rite, but it's not unique to the Bari roll. It is also found in BAV Vat lat 10673, Vat lat 10657 (palimpsest), Benevento 38, and Benevento 40.
This Bari roll, interestingly, ms probably the only surviving compete and unmixed document of the old Beneventan rite.
That was indeed my fault. "The unique version" was less referred to the composition of the tractus (it is very close to the simple version in the other manuscripts, not to the elaborated one) than to the composition of the ceremony itself.
But how will you put its uniqueness, as "Old Beneventan" (then what is the version in Ben 40 supposed to be?) or as a local rite connected with the episcopal church of Byzantine Bari, shortly before a bigger one was built after the late papal confirmation of the archdiocese?