Q. 1. I noticed at our Church that the Saturday morning Mass readings are different than the Saturday night Mass readings. My understanding as to why the Saturday night Mass readings are different, it is because they are the Sunday readings. As such, those attending the Saturday night Mass are considered to have fulfilled their Sunday obligation to attend holy Mass.
What would happen if the Saturday readings were read on Saturday night? Would those present still qualify as having fulfilled their Sunday obligation of attending Holy MasS? A. 1. On this matter, the Catholic Church Canon Law states: "The obligation of assisting at Mass is satisfied wherever Mass is celebrated in a Catholic rite either on a holy day itself or on the evening of the previous day." [canon 1248 §1]
Attending Holy Mass on the evening of the previous day is all that is required to fulfill one's Sunday obligation of attending Holy Mass. It is not necessary to have the Sunday readings in order for the Saturday night attendance to be valid. It is only necessary that the readings are appropriate for the day on which the Holy Mass is being celebrated in accordance with the liturgy.