Assessment of non-filers: officer may assess tax to best judgment; filing a valid return withdraws the order but interest and fees persist. Where a registered person fails to furnish the return even after notice, the proper officer may assess the tax liability to the best of his judgment using available material and issue an assessment order within five years from the date specified for the annual return. If a valid return is furnished within thirty days of service of that assessment order, the order is deemed withdrawn, but liability for interest and late fee continues.