Obsolescence of Declaration Forms C: specified Forms C declared invalid, disallowing their use for inter state tax compliance. Under the authority of sub rule 13 of rule 5 of the CST (Delhi) Rules 2005, specified Declaration Forms 'C' are declared obsolete and invalid for all purposes with effect from their date of issue; the notification lists reference number, issuer and recipient names and TINs, party address, value stated, tax period and the cancellation effective date, and thereby requires that the listed Forms C not be used for inter state tax benefits or statutory compliance.