"A person familiar with the notices, who asked not to be identified because they weren’t authorized to speak publicly, said the action to close airspace over a major U.S. for security reasons over extended period hasn’t happened since immediately after the terror attacks of Sept. 11, 2001."

https://elpasomatters.org/2026/02/11/unexplained-faa-order-s...

It shows how bad the lack of available sources is, when they interview someone familiar with the type notice in general, but not this specific notice.