Commentary for Numbers 36:5

ויצו משה את בני ישראל, Moses commanded the children of Israel, etc. The meaning of the verse is that Moses commanded them at the behest of G'd who had commanded him to address the children of Israel. What was the content of that command? "The tribes of the sons of Joseph are correct in what they are saying." The whole verse is a compliment to the tribes of Ephrayim and Menashe.

Correctly are the descendants of Yoseif’s tribe speaking. Even though in any case this claim was not effectual except for that generation, that is because the holiness of the Land is not uprooted after it has already been completely defined, for the sake of a minority, and the Yoveil will also not be uprooted because of this. However it is fitting that the initial entry and fixing of the holiness should be in the best way possible, therefore in that generation the claim was justified.