Revocation of cancelled registration: applications permitted only after filing outstanding returns and completing interim returns within thirty days. A Removal of Difficulty Order granted a one time opportunity to apply for revocation of registration cancellations; rule 23 provisos require that returns due up to the cancellation date be filed and amounts paid before filing an application, and that all returns for the period between cancellation and revocation must be furnished within thirty days of the revocation order; a further proviso allows applications despite portal restrictions for retrospective cancellations provided returns for the intervening period are filed within thirty days of revocation.