Nothing herein contained shall affect such rights, if any, as may have been acquired under any law of the United States by any person in lands subject to this subchapter and such rights, if any, shall be governed by the law in effect at the time they may have been acquired: Provided, however, That nothing herein contained is intended or shall be construed as a finding, interpretation, or construction by the Congress that the law under which such rights may be claimed in fact applies to the lands subject to this subchapter or authorizes or compels the granting of such rights in such lands, and that the determination of the applicability or effect of such law shall be unaffected by anything herein contained.