The nearest I've got to old notation systems are the tunes reproduced in the Dover edition (1967) of a translation (1948) of Arbeau's Orchesography (1589). That took some sorting out (especially since it is published sideways -one note for each dance step description.

Choirparts are free Youtube videos, that show the score on the screen. BUT there seem to be various versions of the doublechoir parts of the Mass - the notes are all there but different people sing them. I.e. the score is not the same as the onee are singing from.