Units with the second digit of 0 are usually sergeants and above.
Unit #000 would be the region commander (a major I think), then sequentially from there are the subregion commanders. 5001, is the captain in charge of the region 5, subregion 1 office. 5002, the captain in charge of the region 5, subregion 2 office, etc. Usually for sergeants, the third digit indicates the subregion they belong to, so 5047 would be a a region 5 sergeant, in subregion 4, the 7th highest sergeant in that subregion.
This is how I understood it to be, back in the days before they changed their regions.