In deciding what steps (if any) were reasonable, the WRA must consider whether the taxpayer knew, or should have known, about the under-determination or under-assessment.
Wrth benderfynu pa gamau (os o gwbl) sy’n rhesymol, rhaid i ACC ystyried pa un a wyddai’r trethdalwr am y tanddyfarniad neu’r tanasesiad, neu a ddylai fod wedi gwybod amdano.