Municipalities (munibr) are supposed to be nested in mesoregions (mesobr). However, there are some municipalities belonging to several mesoregions due to the harmonization and confidentialization of the variable munibr.
In years 1980, 1991 and 2000, when I look at municipalities that have not been harmonized nor confidentialized (munibr with code ending by a number smaller than 99900), I logically find that each one of those belong to one mesoregion (ie. they are nested in mesoregions).
However, this is not true in 2010. I find this weird. Does any one have an explanation?