The sins of mankind (thus, all were “saved”) were forgiven on Good Friday.
Jesus, Himself made the pronouncement: “It is finished.”
Thus, the body of Christ was already formed before the Day of Pentecost, as those who assembled together on the Day of Pentecost were already believers that Jesus was the messiah and the risen and ascended savior and had accepted Him for salvation of their souls. Thus, the body of Christ was already born before the Day of Pentecost. The body of Christ was already formed...
And thus, their speaking with other tongues on the Day of Pentecost was a distinct act, subsequent to their salvation.
The formation of the Body of Christ, then, took place and had taken place before they spake with other tongues.
Thus Baptists are incorrect that the Body of Christ was formed or born on the Day of Pentecost.
The Body of Christ was already in existence before they spake with tongues and before the Day of Pentecost even.