No SCOTUS cases on point? I would think someone would have tested this vis a vis the Full Faith and Credit clause.
Nobody has been brave enough to test the law.
You'd have to have a valid permit from your home state, travel to another state that doesn't recognize your state's permit, and get arrested for possession of a concealed firearm in order to have a case that could eventually work its way up to SCOTUS.
Are you volunteering to travel to New York City and get arrested for illegally carrying a concealed firearm?
There was a case in 2013 of a woman, Shaneen Allen, who had a permit to carry a firearm in her home state of Pennsylvania, but took a wrong turn in Philly and accidently got stuck on a bridge and had to drive into New Jersey to turn around, where she was arrested for illegal possession of a firearm.
She struck a plea deal with New Jersey, then Governor Krispy Kreame issued her a full pardon.
So that could have been a Full Faith and Credit case, but was not pursued.