No deed to any lot in such unincorporated town or unincorporated government townsite entry shall be made or delivered to any alleged occupant thereof before proof shall have been made under oath, showing such claimant to have been an occupant of such lot or parcel of land within the meaning of said laws of congress at the time of the entry of such townsite at the proper United States land office, but the grantees, heirs, executors, administrators, successors in interest or assigns of such occupant of any lot, as such, may receive such deed.