God has always given credentials to those he is using as his spokespersons.
He gave credentials to Moses: Parting Red Sea; 10 Commandments etc.
In the first century he gave credentials to the Christian Congregation on Pentecost 33 CE buy the miraculous gift of tongues.
Our recent Bible Study in the Draw Close to Jehovah book chapter 4 paragraph 16 stated: "Although now is not his time for performing miracles, Jehovah has not changed since Elijah's day" So today, we have no miracles that make it so easy to identify Jehovah's representative as was the case in the days of Abiram. He had clear proof that Moses was representing Jehovah.
It makes the point that the GB really doesn't have the same credentials without explicity saying that. Might cause some to think.