So, someone please correct me if I’m wrong: The Jewish Passover Seder was to be on Friday that year. In anticipation of His sacrifice on the cross, our Lord celebrated the Last Supper and instituted the Holy Eucharist on Thursday. Since, on the next day, He was the one, true and final Passover sacrifice, the Holy Lamb of God, then the Last Supper was, in anticipation, sacramentally the same sacrifice. In that sense, it was not only a Passover meal, but THE Passover meal, to be perpetuated until the end of the world.
Although the Seder was not celebrated by the other Jews on Thursday that year, the Last Supper (which was the Holy Sacrifice on the Cross in anticipation) was indeed the fulfillment of all Passover Seders.
I hope I got that right.