Again, semantics. You have twenty people in the congregation, ten years later there are only ten left, so you assume the ten who are no longer there were unsaved because they didn't persevere.
That is a cruel way to look at it. Perhaps they aren't there anymore because in your midst is someone quite evil, they discovered it and left?
Have you considered these verses before? They indisputably tell us that it is God alone who made Himself guarantor of faith and salvation of those whom He had preordained unto salvation. Therefore, those who fall away, do so because were not of those who are kept by the power of God - not everyone is.
[1Pe 1:4-5 KJV] 4 To an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you,
5 Who are kept by the power of God through faith unto salvation ready to be revealed in the last time.