the date on which a relevant appeal (in the course of which the ground could have been put forward) was determined by a court or tribunal, or is treated as having been so determined
y dyddiad pan ddyfarnodd llys neu dribiwnlys ynghylch apêl berthnasol (y gellid bod wedi cyflwyno’r sail fel rhan ohoni) neu’r dyddiad y mae i’w thrin fel pe bai wedi ei dyfarnu felly;