However, since 2021 nearly all data has been self-reported, rather than being carbon monoxide monitored and may impact direct comparisons prior to this.
Fodd bynnag, ers 2021 mae bron yr holl ddata wedi cael ei hunan-adrodd, yn hytrach na bod carbon monocsid yn cael ei fonitro, a gallai hynny fod wedi effeithio ar gymariaethau uniongyrchol cyn hyn.