This is my first post containing Mass Ordinary parts. In the old Kyriale, there are 18 different Mass ordinaries (each containing a Kyrie, a Gloria, a Sanctus, and an Agnus Dei) for different Masses throughout the year. These are typically based on ancient chants (such as tropes) that were once used in the liturgy but fell out of use over time. For instance, Mass 1 is called Lux et Origo after the trope which begins with:
When translated this means, "Light and origin of light, Most High God, have mercy." This chant Mass is traditionally sung during Paschaltide. In addition, there are 6 Credos, as well as several ad libitum Mass parts including 11 Kyries, 4 Glorias, 3 Sanctuses, and 2 Agnus Deis.
NB: Be aware that the Kyrie differs slightly in the Extraordinary and Ordinary Forms of the Roman Liturgy. In the EF, Kyrie eleison is sung 3 times, followed by Christe eleison 3 times, and then Kyrie eleison 3 times, whereas in the OF, each phrase is sung only twice. My Kyrie recordings will always be according to the EF pattern. In order to make the Kyrie suitable for the OF, remove the middle time it is sung (the specific choice of which phrase to remove typically has an effect in the last set of 3 sung Kyrie eleisons).