It does pay to know your local codes...
Sure, if you install an AFCI in a place where it is not required, there is no violation. There was no prior rule saying 'not to do it.'
If you want to Romex a four story building, then you might have an issue, as rules for the use of NMC 'loosened up' some.
You can only be cited for violating the adopted code.....if you happen to comply with some other code- so what?
