I believe they can't because of the legality, it would remove the secrecy of the warrant. The canary allows a company to imply they got searched without breaching the secrecy.
In this case, information got removed, which is not illegal because the information removed is not required by law.
It's not so much that the information got removed but rather they decided to not update the message. Failure of a new update is the signal that something happened.
So if they're allowed to reveal they got searched, why the need for the canary? And if it works on a company level, why does it not work on a user level?
In this case, information got removed, which is not illegal because the information removed is not required by law.