Have you looked through your state's UCC, Article 9? I have not had much time to look but if there is a 60% rule in your state, it should be there. I did some looking on CB but all I could find was "most states" honor this rule. Have not found a list or anything concrete yet.
Also I know you said you looked at Why Chat's site but did you go through the
repo deficiency links?
I know that may not be much help but try reading really well through those links and when I get some time, I will try to as well.
I also checked on the bank closing your CCs just because of this repo and found out
they can do that. So, just want you to be aware of that.