Wikipedia does claim that patriot act subpeonas can penalise any disclosure of the subpeona. But i am not a lawyer, and afaik this is untested (or at least undisclosed :/ )
In September 2014, U.S. security researcher Moxie Marlinspike wrote that “every lawyer I’ve spoken to has indicated that having a ‘canary’ you remove or choose not to update would likely have the same legal consequences as simply posting something that explicitly says you’ve received something.”
I think my point is that a gag order with a long time out essentially kills the canary, even if it doesnt affect the vast majority of the services users.
Thanks for your response though, I appreciate the additional information.