Do the dead who have no Masses said for them miss out on graces?
The short answer
No. All the dead are prayed for at every Mass — Eucharistic Prayer IV, for instance, prays for all the departed. God is just and merciful; no one goes wanting for his mercy.
At every Mass
All the dead are prayed for at every Mass. Eucharistic Prayer IV, for example, asks God to remember those who have gone to their rest in hope of rising again, and all the departed.
God's mercy
God is just and merciful. No one goes without his mercy.