Vox clamantis in deserto

Source: 
Hanover, NH, Dartmouth College Library, Rauner Codex MS 003203
Folio: 
029v
Sequence: 
1
Feast: 
Thomae Apost.
Office/Mass: 
V
Genre: 
W
Position: 
R
Cantus ID: 
008246
Mode: 
*
Manuscript Reading Full Text (standardized spelling): 
Vox clamantis in deserto
Manuscript Reading Full Text (MS spelling): 
Vox clamantis in deserto
Indexing notes: 
I am concerned that the feast is incorrect, as the Cantus ID is for a chant for the first Sunday in Advent, whereas ours seems to be part of the feast of St. Thomas. The rubric in our MS reads "Pro com | memoratione | adventus | Antiphona"; am I correct in making this part of the same feast of St. Thomas?