Parshas Bamidbar begins with the apparent appointing of 12 nesiim (princes) who would help Moshe with the counting (and presumably have some other administrative or authoritative role). Parshas Naso discusses their contribution to the Mishkan.
However, there's a bit of an issue here: the events of Parshas Bamidbar occurred in the second month (Iyar) of the second year, and the setting up of the Mishkan and subsequent princely gifts began on the first month - before their appointment!
The pesukim at the beginning of Bamidbar seem to imply that Moshe was told to appoint them specifically for/at the time of the count, but Parshas Naso implies otherwise. Were they actually appointed (or otherwise known) before the Parshas Bamidbar counting? (I'm inclined to say yes, but I'd like to see the issue discussed somewhere)