Accompanying any ordinance for a local improvement presented by the board of local improvements to the corporate authorities shall be a recommendation of such improvement by the board, signed by at least a majority of the members thereof. The recommendation by the board shall be prima facie evidence that all the preliminary requirements of the law have been complied with. If a variance is shown on the proceedings in the court, it shall not affect the validity of the proceeding, unless the court deems the variance willful or substantial.