What are "Sarei ha'Nitzavim"?
Rashi: They are taskmasters and officers over the workers.
Here it says that there were 3,300 taskmasters. In Divrei ha'Yamim II, 2:17 it says that there were 3,600. Below (9:23) it says that there were 550 Sarei ha'Nitzavim on the Melachah, and in Divrei ha'Yamim II, 8:10 it says 250!
Rashi: The 3,300 were appointed over the 150,000 workers - each was over 45 [or 46] workers. Another 300 were appointed over everyone; each was over 500 workers. Below it discuss those appointed over native Yisraelim working in store cities. There were 250 taskmasters over them; Divrei ha'Yamim counts them alone. Below they are joined with the 300 taskmasters over all the 150,000 workers, so it says 550.
Radak (29): Divrei ha'Yamim II, 2:17 includes 300 taskmasters appointed over the taskmasters. This is like Shotrim and Nogshim 1 .
Malbim (here, and 9:23): There were 3,000 appointed over the 150,000 workers - each was over 50. Another 300 were appointed over 500 each. Here it counts both of them. Divrei ha'Yamim counts also 300, each of whom was appointed over 10 of the 3000 appointed over 50 workers. Shlomo counted 150,000 who converted after David counted the converts. There were also 25,000 from before David; there were 500 appointed over 50 each, and another 50 over 500 each; in all, there were 550. Divrei ha'Yamim II, 8:10 does not mention Sarei ha'Nitzavim. Rather, it discusses taskmasters over the 10,000 Yisraelim working in Levanon. There were 200 over 50 workers each, 20 over 500 each, 20 over the 200 taskmasters, and 10 over 1000 workers each; in all, there were 250.
Shemos 5:6 mentions both of them. Below (9:23), Radak resolves the contradiction about the number of Sarei ha'Nitzavim like Rashi did (refer to 5:30:2:1. - PF)
