Chapter 36

The daughters of Zelophehad from the tribe of Joseph were required to marry only in their own tribe, so that their inheritance, which God himself commanded that they receive, would not be transferred to other tribes by the right of male heirship.  Daughters did not inherit, even what was theirs before the marriage.  This appears to be a unique instance, not a standing rule, since the daughters of this one "original" clan are specifically referenced.  But there is an implication that in similar situation down through time, land that belonged to one tribe originally could never become the inheritance - or move at jubilee - to a different tribe.  And rather than doing a lot of paperwork and record keeping to make sure what had originally belonged to whom, the rule was that women who's father's had no sons to inherit his land could only marry within their tribe, which insured that even though the land might change families, it would never change tribes.

They couldn't enforce this anymore.  The records no longer exist for Israel to trace its ancestry back to the original 12 tribes.  But according to Ezekiel, during the Millennial, the land will be divided again according to the 12 tribes.  So somehow, presumably by supernatural means, the Jews alive in the Millennial will know where they came from.