This question is similar to the date of PhD award in France, but for the case of Oxbridge (maybe all of UK, but I don't know).
There is the date of the defense (behind closed doors), after which one may recieve no corrections, minor corrections, or major corrections (re-submit thesis). After the corrections are done the thesis is given to the University, and one can be "approved" for a PhD. But one only receives the certificate after a graduation ceremony, which may be years (typically weeks or months) later.
Which of these dates should I choose for fellowship applications etc? I have
- Date I defended
- Date I submitted the last version of the thesis
- Date thesis was approved
- Date I left the university to work elsewhere (become a postdoc)
- Date I graduated. (This is on the official transcript.)
In this chronological order. I obviously don't care personally, but often there are requirements such as "this and that many years after your PhD".