As each tribe acquired its inheritance in the Land of Canaan, it would get down to seven tribes yet to receive their inheritance, even as the number grew and it could be said that seven tribes had received their inheritance.
Joshua 18 says,
But there remained among the children of Israel seven tribes which had not yet received their inheritance (Joshua 18.2).
However, they eventually all received their land. This text does not seem to point to any significance in the number seven associated with the number of tribes yet to receive their inheritance during that time in history.