Lotteries #3 and #4, per day in the Beit HaMikdash! For the ketoret, incense, only those who had never done it before were eligible. A blessing of prosperity reaches those who have done it, so once seems to be enough. But the kohanim weren't eligible to do it very often to begin with, so the extra motivation to limit it to once ever may have other factors as well. Plus, the tribes that produce Torah scholars: Levi and Yissachar. But it's not clear how accurate that was (what about Yehudah?? What about Yissachar missing, as one of the 10 tribes)... Also, how many kohanim were to be involved in the daily handling of the sacrifices (from 9 to 12). Including why the water libation on Sukkot would take place in the morning.