I do not believe that a canary can be a reasonable defense for "Oh I didn't say anything"
There's two situations here: Either the gov't doesn't care that you say you got an NSL (without specifics on time/subject), or they do care.
If they do care, discussion with judge:
- Did you say you got an NSL, despite there being a gag order?
- Well I didn't not say anything
- You had previously had a communication strategy set up to communicate when you would get an NSL
- ...
- So you did say it.
Case where the gov't doesn't care that you mention you got one (given you hide the time/subject through delays):
- Why did you do all the crazy stuff to tell people instead of just telling people?
- It was funner this way
Is the canary really a legal defence? I can only imagine that no, it isn't. At best it lets you imply that you got an NSL even if you didn't (oops we removed it from the template). At worst you're facing the same legal issues as before