The Research Executive Agency does not have a clear-cut definition for 'possession of the doctoral degree'. It can largely vary from one national education system to another (or even in the same country from one university to another). In theory, this could be when the degree is conferred by the university either in notice by letter or by ceremony (whichever comes first). Prior to that, the official status of the defendant is that of a graduand.
In some universities, there is an obligation to attend the graduation ceremony, in others not. In British universities, e.g. the relevant point is when the result of the viva is published (normally a couple of weeks after the viva). The graduation could be then 6 months after the publication, but in the certificate the date of the award will be the publication date rather than the date of the graduation ceremony. In Germany, however, not all universities grant successful PhD defendants the right to hold a "Dr. des." Title until the degree is officially conferred.
For all these reasons, the 'possession of the doctoral degree' is analysed on a case-by-case basis during the eligibility check. In case there is any further information needed, applicants will be contacted directly by the REA services and requested to provide all necessary supporting documents.
(Answer provided by REA)