All neumes are not created equal.
In "Musical Quarterly" Vol. 38, (Jan. 1952), author Egon Wellesz presents an article, "Early Byzantine Neumes." He begins by mentioning that he has compared "the various phases of Byzantine musical notation from the 9th century to the end of the 13th." Generally, he explains that the neumes in MSS from different centuries present the same melodies, but they do not express those melodies in the same way. in the 1000's, dots and dashes (probably something like staccato and tenuto marks) were introduced, and old ekphonetic signs were given different meanings. Rhythmical signs were turned into interval-signs. (Maybe this would be like turning a "hold-this-note" fermata sign into a quarter-rest, in modern musical notation.)
So if we try to date an undated medieval MSS that has neumes, we might be able to zero in on a more precise date if neumes are in the equation -- not just the presence of neumes, but the *kinds* of neumes -- by comparing the neumes in the Biblical MSS with the sorts of neumes that developed in different stages in music-MSS.
Yours in Christ,
James Snapp, Jr.