The roll prepared by the Secretary shall show for each Native, among other things, the region and the village or other place in which he resided on the date of the 1970 census enumeration, and he shall be enrolled according to such residence. Except as provided in subsection (c) of this section, a Native eligible for enrollment who is not, when the roll is prepared, a permanent resident of one of the twelve regions established pursuant to section
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(a) of this title shall be enrolled by the Secretary in one of the twelve regions, giving priority in the following order to—
The Secretary may enroll a Native in a different region when necessary to avoid enrolling members of the same family in different regions or otherwise avoid hardship.