REVENUE MEMORANDUM CIRCULAR NO. 18-2007 issued on March 16, 2007 notifies the disposal of old blank Tax Credit Certificates (BIR Form Nos. 2310 and 2320) and Tax Debit Memo s (BIR Form Nos. 2311 and 2321) listed in the Circular. The listed accountable forms have been cancelled and all official transactions involving the use thereof are considered as invalid.