In the absence of any intervening valid adverse interests any assignment made between June 23, 1910, and January 1, 1913, of land upon which the assignor has submitted satisfactory final proof and the assignee purchased with the belief that the assignment was valid and under section 441 of this title, is confirmed, and the assignee shall be entitled to the land assigned as under section 441 of this title, notwithstanding that said original entry was conformed to farm units and that the part assigned was canceled and eliminated from said entry prior to the date of final proof: Provided, That all entries so assigned shall be subject to the limitations, terms, and conditions of the reclamation Act, and Acts Amendatory thereof and supplemental thereto, and all of said assignees whose entries are confirmed shall, as a condition to receiving patent, make the proof required, prior to May 8, 1916, of assignees.