Warrant canaries are so vague that it may technically breach the gag but it doesn't give any information that the gag orders attached to/in NSLs mainly that the targets of NSLs can't find out that their information was requested. Once a year site/company wide canaries provide no actionable information and don't even threaten to expose abuses that would show up as an inordinate number of letters being sent to a particular company that I doubt the government really cares about them in the slightest.