Comentario citado sobre Números 4:36

והלוים...לא התפקדו בתוכם, “But the Levites’ census was not included in that of the other twelve tribes.” Nachmanides writes, that notwithstanding the fact that up until then no directive had been given to count the Levites separately and according to different criteria, Moses realized on his own that he was not meant to include them as an integral part of that census. One of the reasons was that whereas a leader had been named for each of the other tribes, no one had been appointed as the leader of the tribe of Levi. At any rate, while Moses was in doubt how to proceed, he would not arrogate the decision to himself, and as soon as he had concluded the counting of the other twelve tribes, G’d told him how to proceed with the Levites. He called Aaron, in order to give him the honour, seeing that he was the de facto leader of the tribe. Perhaps this is the reason why we find dots on the word ואהרן (verse 39) i.e. a hint that Aaron was in Moses‘ company when G’d told him how to count the Levites. Subsequently, in 4,46 as well as in 4,36 and 4,45 we are also told about the respective leaders’ presence during these counts, as everything had to be done with the approval of all the notables concerned. The same applied to the division of the tasks to be performed by the various groups of Levites, each group headed by descendants of one of the three sons of Levi, son of Yaakov.