Also, even where collections went ahead the coronavirus (COVID-19) pandemic may have had further implications on the quality of the data which might not have been immediately apparent.
Hefyd, hyd yn oed pan aeth casgliadau yn eu blaen, mae'n bosibl bod pandemig y coronafeirws (COVID-19) wedi cael goblygiadau pellach ar ansawdd y data na fyddai wedi bod yn amlwg ar unwaith.