I have to politely disagree unless you can provide a scriptural reference to verify that statement.
If God is omniscient, and He is, there can be no doubt that He knew who would be saved and who wouldn't long before He created the universe. Actually, He knew that in eternity past, which is beyond our ability to comprehend. Therefore, nothing that happens on planet Earth before Jesus Christ returns could or will take Him by surprise, including who will be the last man or woman who will accept His Son Jesus Christ as Lord and Savior and thereby complete the Body of Christ, aka His Church.
Here are 7 scriptural references. I copied and pasted from the Catechism because I'm lazy, and because I don't believe in debating theology the same way you do. But if you read the Scriptural references at the bottom, and pray before reading, I'm sure you'll find the answer you seek.
The glorious Messiah's coming is suspended at every moment of history until his recognition by "all Israel", for "a hardening has come upon part of Israel" in their "unbelief" toward Jesus.569 St. Peter says to the Jews of Jerusalem after Pentecost: "Repent therefore, and turn again, that your sins may be blotted out, that times of refreshing may come from the presence of the Lord, and that he may send the Christ appointed for you, Jesus, whom heaven must receive until the time for establishing all that God spoke by the mouth of his holy prophets from of old."570 St. Paul echoes him: "For if their rejection means the reconciliation of the world, what will their acceptance mean but life from the dead?"571 The "full inclusion" of the Jews in the Messiah's salvation, in the wake of "the full number of the Gentiles",572 will enable the People of God to achieve "the measure of the stature of the fullness of Christ", in which "God may be all in all".573
569 Rom 11:20-26; cf. Mt 23:39.
570 Acts 3:19-21.
571 Rom 11:15.
572 Rom 11:12, 25; cf. Lk 21:24.
573 Eph 4:13; 1 Cor 15:28.
God acts on earth in many ways, including through human instruments.