Matthew Poole and continuators on Numbers 7:87

87 All the oxen for the burnt-offering, were twelve bullocks, the rams twelve, the lambs of the first year twelve, with their meat-offering : and the kids of the goats for sin-offering twelve.

Which was not mentioned before, because it was sufficiently understood from the Law which required it, Numb. 15. 3, 4, 5. but for greater assurance is here expressed.