For this reason, many of the following conclusions are drawn on the basis of pre-pandemic evidence or recent data which is not wholly compatible with data captured prior to the pandemic.
Am y rheswm hwn, mae llawer o’r casgliadau canlynol yn cael eu llunio ar sail tystiolaeth cyn y pandemig neu ddata diweddar nad yw’n gwbl gydnaws â data a gasglwyd cyn y pandemig.