Apologies to the confused. This medieval term for the Festival of the Holy Cross was indeed used for the Feast of its Invention [Finding] in May. Since that Feast is abolished in the NO Calendar, I have tended to keep the word alive by apply it to the surviving Feast of the Cross in September.
The abolition of the Invention was a great shame; not only because it was so popular a feast in the Middle Ages, but because it is good to reflect on the Cross in Eastertide; letting our appropriation of Resurrection illuminate the Passion and remembering that Passion and Resurrection are two sides of one coin. I believe S Margaret Mary believed our Lord wanted a feast of the Saqcred Heart in Easter Week.