if the increase took place on or before 22 July 2004, the increase in the partnership share was effected by an instrument stamped with ad valorem stamp duty, or
os digwyddodd y cynnydd ar neu cyn 22 Gorffennaf 2004, daeth y cynnydd yn y cyfranddaliad partneriaeth i rym drwy offeryn a gafodd ei stampio â threth stamp ad valorem, neu