After the Board of Review has completed its review of the assessment roll, and not later than the first Monday in April, the majority of its members shall endorse thereon and sign a statement to the effect that the same is the assessment roll of the City for the year in which it has been prepared. The omission of such endorsement shall not affect the validity of such roll. The roll, as prepared by the City Assessor, shall stand as approved and adopted as the act of the Board of Review except when changed by a vote as herein provided.