Revocation of cancellation of registration: filing allowed with required returns and thirty day compliance for retrospective cancellations. Clarification sets procedural conditions for filing applications for revocation of cancellation of registration: applicants must furnish all returns due up to the date of cancellation and pay any amounts due before applying; returns covering the period from cancellation to revocation must be filed within thirty days of the revocation order; and where cancellations are retrospective and the portal prevents filing, a proviso permits revocation applications provided returns for the retrospective period are furnished within thirty days of revocation.