In the eyes of a court, either it's reasonable to infer that a disclosure notice compliant with the Dep. A.G. letter is a sign of having received a NSL, or it isn't. If it isn't, then the court can have no objection to such a notice. If it is reasonable to make that inference, then the Dep A.G. letter amounts to a formal authorization from USG to issue a document permitting that inference.

In the eyes of the internet at large, a 0-249 notice never actually means 0 – by the Gricean maxim of quantity, if a range is given then it can be assumed that it was necessary that a range be given.

This is the problem: if you set up a codebook of "perfectly legal things to say," it doesn't mean you escape gag order by using that codebook to talk about things in the gag order.

Here's a hypothetical (which someone has probably already suggested):

Say the reddit admin who puts this report together always includes a number from 0-999 at the very end of the report. To that admin, it's a signal of a gag order having been imposed. Maybe when it's an odd number, or when it's prime, or when the middle digit is the sum of the two outer digits, or the number is greater than 900.

If only that admin knows the system, everything is okay. But it's also useless as to what a warrant canary is used for: telling users you've been subject to a gag order.

So the admin tells people that it's intended as a canary and the method to decode. It's pretty obvious this is communicating exactly the information that you've been forbidden to communicate.

So if the Internet community decides that "we have received no NSL letters" means no NSL letters and "we have received 0-249 NSL letters" means there has been an NSL letter, than changing your message to comply with that understanding is an obvious communication.