Numbers 36:4

And when the jubilee of the children of Israel shall be, then shall their inheritance, that of Zeiophehad's daughters, be put unto the inheritance of the tribe whereunto they are received, by the fact of their marriage; so shall their inheritance be taken away from the inheritance of the tribe of our fathers. Until the Year of Jubilee there was always a possibility of a childless marriage or of the sale of the property to members of the tribe of Manasseh; but after the Year of Jubilee the last chance would be gone, and relief would no longer be possible.