Thank you for this post. People seem to be treating warrant canaries as a sort of “gotcha!” defense that no judge would take seriously, but you’ve given a good explanation of why it’s not.
It should be noted that there is currently no public case-law on whether warrant canaries are actually legal. So really, until this topic goes before a court in a benchmark case, your guess is as good as mine.
I agree there are several theoretical reasons why warrant canaries might actually be a useful tool, but it's just as likely that intentionally constructing a scenario where you are implicitly telling people about a gag order through a bunch of hurdles would not be considered following the spirit of the law.
For instance, if you get an NSL you can't tell your family about it. When going to see your lawyer, you need to omit the reason why you're seeing a lawyer -- which is basically de-facto requiring you to actively lie to your family (because "I can't tell you why I'm seeing my lawyer" is arguably code for "I have received an NSL" if your family is aware that you might get an NSL one day).
I personally think this is massively unjust (and in Australia, we have explicit laws to disallow speaking about the existence or non-existence of any such secret warrants -- which makes even attempting to set up a warrant canary a crime with a minimum 2 year sentence).
