It is an interesting question because in their physical absence there is no one to authorise. They didn’t give the charge of authorising any spokesperson to anyone.
But personally I waited to get clear indication that it is Her Will sanctions me this work. Until the sure sign came (and quite a few of them) i refused and resisted speaking about them. It is only when I received a clear inner command from the Mother as the ‘spokesperson for Sri Aurobindo’ that i started speaking. Time and circumstances have only confirmed this inner revelation.