On documentation, if the FBI was already infiltrating it then, I bet there's a lot of information on membership in FBI files.
To join the KKK, Byrd sword an oath before God to uphold the KKK Constitution. Among other things that Constitution says that each member swears:
"To maintain forever white supremacy."
"To maintain forever the God-given supremacy of the white race."And...
Every Klansman has unqualifiedly affirmed that he will "faithfully strive for the eternal maintenance of white supremacy."
In my brief research on this topic, and having viewed various versions of past KKK Constitutions, I see no provision for leaving the Klan once sworn unless expelled. Until Byrd can demonstrate otherwise, he is still a member of the West Virgina KKK and is still under oath of allegiance to the Klan.
...Like that will matter at all to the Rats.