The value for January to March 2020 will have already been subject to some of this downward revision, whereas the equivalent figure for January to March 2021 will not yet.
Bydd gwerth Ionawr i Fawrth 2020 eisoes wedi bod yn destun rhywfaint o ddiwygio am i lawr, ond nid yw’r ffigur cyfatebol ar gyfer Ionawr i Fawrth 2021 wedi cael ei ddywygio eto.