The next time anyone asks you that question, if you have your Bible handy, read them John, Chapter 3 and Chapter 17.
Verse 8 is particularily potent:
"The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit." (JOHN 3:8)
"I have manifested thy name unto the men which thou gavest me out of the world: thine they were, and thou gavest them me; and they have kept thy word. Now they have known that all things whatsoever thou hast given me are of thee. For I have given unto them the words which thou gavest me; and they have received them, and have known surely that I came out from thee, and they have beleived that thou didst send me. [b] I pray for them: I pray not for the world, but for them which thou hast given me; for they are mine[/b]. And all mine are thine, and thine are mine; and I am glorified in them." (JOHN 17:6-10)
Also, "Hearken unto me, ye that know righteousness, [b]the people in whose heart is my law[/b]; fear ye not the reproach of men, neither be ye afraid of their revilings." (ISAIAH 51:7)
Also, "But [b]the natural man receiveth not the things of the Spirit of God[/b]: for they are foolishness unto him: neither can he know them, because they are spiritually discerned." (I COR 2:14)
edit: Even if there is evidence of someone back then claiming to be born again, there's no way to prove or disprove who's born again and who's not - except maybe by their fruit.