The value for January to March 2019 will have already been subject to some of this downward revision, whereas the equivalent figure for 2020 will not yet.
Bydd gwerth Ionawr i Fawrth 2019 eisoes wedi bod yn destun rhywfaint o ddiwygio am i lawr, ond nid yw’r ffigur cyfatebol ar gyfer 2020 wedi cael ei ddywygio eto.