Date of PhD award Oxbridge
The multitude of dates that would make sense is not at all specific to Oxbridge, and many funding bodies will clarify which date they want in the fine print.
If they don't specify otherwise, then the graduation date is a safe bet, as this is the date written on the certificate. In my experience, &quot;at most x years post PhD&quot; restrictions are far more common, and for those the graduation date will be the most beneficial one for you anyway.
If its not specified, and if the graduation date would disqualify you, but one of date of defense and submission date for the final version would work, then it makes sense to get in touch with whoever is in charge to make the case that they should consider you.