This is because for non local health board managed practices, locum work is not recorded consistently through WNWRS and all locum data used in these statistics are collected through LHW.
Y rheswm am hyn yw na chaiff gwaith locwm ei gofnodi'n gyson drwy WNWRS a chaiff yr holl ddata locwm a ddefnyddir yn yr ystadegau hyn eu casglu drwy LHW.