One can gain a Plenary Indulgence for a soul in Purgatory everyday if they do a group rosary, like a with the family at home or at the church with other faithful IFthey do an additional Our Father, Hail Mary , and Glory Be for the pope.
In my SSPX chapel, when the priests lead the rosary, they never do the prayers for the pope, nor have they taught the people about the plenary indulgence. Therefore, the only persons gaining the plenary indulgence are those that do it themselves in silence.
Do all the SSPX priest not do the prayers for the pope?