There was a 1-yr (as opposed to the current 3-yr) repeating cycle for Sundays.
For weekdays there were no specific weekday readings as we have with the Novus Ordo Mass (a 2 yr repeating cycle - year 1 and year 2) with the exception of a few times during the year - such as the weekdays of Lent.
On weekdays the Mass readings were determined by the Feast. If there were no Feast that day then the priest would say the Mass of the preceding Sunday, a Votive Mass (several were provided in the Missal such as the Mass of the Holy Spirit, etc.) or the Mass of any Saint could be used as a Votive Mass.
Here is the Lectionary for Sundays and major Feasts.
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