Why does the Torah stress "Heim Nesi'ei ha'Matos"?
Rashi: It is with reference to the slavery in Egypt, when these very same princes served as policemen, to force their Jewish brothers to fulfill their quota of bricks, failing which they were mercilessly beaten. They were now compensated by being chosen as leaders of their respective tribes.
What is the Torah referring to when it writes "Heim ha'Omdim al ha'Pekudim"?
Rashi: It means that they stood together with Moshe and Aharon when they counted Yisrael. 1
Seforno: When they stood by their respective tribes as they were being counted, they felt that some of the members of their tribe were suspected of having sinned. 2
Targum Yonasan: They are the ones who were appointed leaders in Egypt.
Rashi explains 'they stood... when they counted Yisrael.' That was a month later (the Torah is out of order)!
Riva citing R. Tam of Orlins, Sifsei Chachamim: When Moshe wrote the Torah, they had already stood when they counted. This is like "Kidmas Ashur" (Bereishis 2:14. There, the Torah discusses before Ashur was even born; it means, later the place will be called so - Kesuvos 10b.)