Mass intentions for extremely dead people?

I have a question: how long should Masses be said for the repose of the souls of people who have died?

This morning at Mass, the name announced during the usual petition for grace for our beloved dead was, we'll call her, Joan of Arc Turtlebaum.

Her real name is distinctive enough that it catches the ear and must be the same person whom I have heard memorialized at weekday Masses and Sunday Masses for a couple of years now. A fellow Mass-goer happened to mention that she had known Joan, and that she had died over twenty years ago!

These Masses aren't on the occasion of her birthday or day of her death, because I hear her name a lot, all over the map of the liturgical year. (Or every day's a holiday for the Turtlebaum family....)

The Catholic Church has always urged the offering of Votive Masses, during which the special intention is for the repose of the soul of a loved one who has died. Actually, the word "votum" merely means a "special intention" and we should always come to Mass with a very specific intention in our heart, to ponder it in the light of the glory of the Scriptures of that day and the Eucharistic Gift.

(In fact, it can be a very interesting way of "playing Bible Bingo." Instead of letting your Bible fall open to see what God has to say to you at that moment about whatever's on your mind, you wait for the Scriptures of the Mass of that day to speak to you instead!)

Masses for the Dead have their intention directed towards the soul that has gone to Final Judgment, as we implore God's Mercy on that soul. The Catholic Church teaches the beautiful doctrine of Purgatory, which for our non-Catholic readers does NOT mean a final hasty repentance for sins unrepented-for in life, but instead a final purgation or cleansing of the soul before it unites with God in Heaven, since "nothing unclean shall enter Heaven" (Rev 21), and we understand that our intercession for those souls is needed, just as we pray for our brethren still living on earth.

But if a person has been dead a really, really long time, should Masses continue to be said for his or her repose? Do they still "need" them? I know that the soul, being dead, exists in God's Time, not ours, and always needs our prayers, but since we don't yet live in God's Time, should we be directing our prayers for the behalf of others more recently deceased?

I still occasionally am moved to pray for the soul of my father, dead five years, and I ask FOR the intercession of my relatives and friends now (hopefully) in Heaven, but it doesn't jump to my mind or heart to ask the priest to make any particular Mass a special Votive Mass for any of them. Am I being neglectful, or is the family of the above-mentioned Joan just not letting go?