By mid-2021, the rebased population estimate was 66,600 lower than the rolled-forward population estimate, decreasing from 3.17 million to 3.11 million.
Erbyn canol 2021, roedd yr amcangyfrif poblogaeth wedi'i ailsylfaenu 66,600 yn is na'r amcangyfrif poblogaeth treigl, gan ostwng o 3.17 miliwn i 3.11 miliwn.