If you had a canary for 0-99, 100-199, etc, and then removed the canary that didn't match, a court might decide that your decision not to assert that you didn't receive 0-99 canaries was as good as asserting that you did receive 0-99. Whereas, if you have a general canary, you can say you removed it because you just didn't want to use a canary any more.
Having said that, I suspect that a court that's sympathetic to the government might well decide that choosing not to speak is itself an act of speech, and that even if you can't be forced to restore a warrant canary, you can be prosecuted for removing it.
"Every third Tuesday of the month" is a canary whereas "About once a quarter, at our discretion, if Bob from Legal remembers" is useless.
Yes it makes more work for the staff, but if that's a problem then just don't do a canary at all.
Or does that cross some arbitrary legal line?