Yn hanesyddol, mae asiantaethau datganoledig a'r rhai nad ydynt wedi’u datganoli, wedi cael y cyfrifoldeb o adolygu trasiedïau o'r fath, ac mae pob un ohonynt wedi gwneud hynny gan ddefnyddio prosesau, gweithdrefnau, deddfwriaeth a chanllawiau gwahanol. Mae’r rhain yn cynnwys Adolygiadau Ymarfer Oedolion a Phlant, Adolygiadau Lladdiad Iechyd Meddwl ac Adolygiadau Lladdiad Domestig. Comisiynodd Llywodraeth Cymru adolygiad academaidd ac adolygiad ymarferwyr i ddeall yn llawn y cymhlethdodau sydd ynghlwm wrth brosesau adolygu yng Nghymru. Yn dilyn yr adolygiadau hyn, cyflwynwyd argymhellion a'u cymeradwyo gan Weinidogion, a dechreuodd prosiect yr Adolygiad Diogelu Unedig Sengl ym mis Rhagfyr 2019.
Historically, devolved and non-devolved agencies have discharged their individual responsibilities of reviewing such tragedies, all of which did so using different processes, procedures, legislation, and guidance. These included Adult and Child Practice Reviews, Mental Health Homicide Reviews and Domestic Homicide Reviews. Welsh Government commissioned an academic review and a practitioners’ review to fully understand the complexities of review processes in Wales. Following these reviews, recommendations were submitted and agreed by Ministers and the Single Unified Safeguarding Review project commenced in December 2019.