A digression, but I can't stand the phrase "I assist at Mass."
Sounds like "active participation."
Or, "I help the priest at Mass. I'm his assistant. I'll assist him"
I prefer "I go to Mass."
Interestingly, Bishop Sanborn uses the phrase "active participation", and I assume he is looking at it from the most traditional viewpoint.
My St. Joseph Daily Missal quotes Pope Pius XII in encouraging the use of hand held Missals: "...s
o that they (the lay faithful)
may take part more easily ... in the Mass ... that the faithful, united with the Priest, may pray together ....". Also cited is a Decree of the Sacred Congregation of Rites: "...
pray along with the Priest in the very words of the Church".
These would seem to suggest that one should be more involved that to "just go" or "just be in attendance".
When I was growing up pre VII (born in 1951) my general understanding (I'll not take time to find citations) was that a priest could not say Mass by himself (there probable were some few exceptions), he had to have at least one altar server and/or a congregation. When a priest wanted to say a private Mass they would have altar servers come from the parochial school, or a mother would bring her sons to serve and she (and perhaps daughters) would stay to comprise the congregation. Yes, the altar servers were "substituting" for those in the minor orders and clerics-in-choir (which hadn't existed at the parish level for centuries), but they are still only laity, and of no higher rank than those in the pews have. When Mass was said at the convent chapel there were no alter servers, the women religious made the responses and rang the bells.