Failure to make an appropriate adjustment could mean the taxpayer has committed an offence by submitting a return containing inaccuracies and they are liable to a penalty on the inaccuracy.
Gallai methu â gwneud addasiad priodol olygu bod y trethdalwr wedi cyflawni trosedd drwy gyflwyno ffurflen sy'n cynnwys anghywirdebau, ac mae’n agored i gosb ar sail yr anghywirdeb.