If accepted the FI may take a month or more. I don't want to encourage anyone to ask for one when it is not considered as a problem that is nationwide.
Here's one that was found in the NECH commentary and is considered valid today. Others were the reasons why rules were changed. If you look back in earlier handbooks the commentary includes that information.
Formal Interpretation 81-6
Reference: Article 410, Part M
Question: Is it intended that fixtures installed in suspended ceilings be subject to the requirements of Part M of Article 410?
Issue Edition: 1981
Reference: 410, Part M
Date: October 1982