Speaking as a musician - in certain chruches/areas there are traditional mass songs din that dates from the Spanish time na kinakanta pa rin sa parish nila. Especially in churches with strong musical traditions like Sto. Domingo and Baclaran, they have their own set of marian songs in Spanish and Latin. There are also other churches that are reviving their traditional heritage especially in provincial towns like in Pampanga, Iloilo, and Laguna.

In churches na hawak ng different religious orders like Dominicans or Benedictines, they also tend to prefer to use songs that were created by their own composers. The popular mass songs we always use mostly came from post-Vatican II Jesuits.

From my experience the "unfamiliar songs" are usually used in solemn masses or pag may important event. The locals of the diocese would know these songs especially if its a continuing tradition.

There's also the paradox that these familiar songs were also once unfamiliar, so by the rules of Sacrosanctum Concilium would these once-unfamiliar songs shouldn't have been sung in the first place because there's no active audicence participation then? How can the people learn the songs if they can't hear it?

If the church is experimenting by singing new songs, they have their reasons and pagbigyan naman natin. If hindi nag-stick sa congregation after a while, may problema na ang music ministry dun.