The value for October to December 2019 will have already been subject to some of this downward revision, whereas the equivalent figure for October to December 2021 will not yet.
Bydd gwerth Hydref i Ragfyr 2019 eisoes wedi bod yn destun rhywfaint o ddiwygio am i lawr, ond nid yw’r ffigur cyfatebol ar gyfer Hydref i Ragfyr 2021 wedi cael ei ddywygio eto.