DN: Some institutions enroll PhD candidates in doctoral programmes only once a year (in October) but job contracts based on the Doctoral Networks Grant Agreement can start earlier. Can beneficiaries apply for funding of person-months before October if the fellow is involved in project activities and has signed a job contract?

Projects decide when they should enroll the doctoral candidates (usually around M6 but they have some flexibility between M1 and M12 of the project). 

The months from the start of the job contract become eligible as soon as the doctoral candidate is registered as a PhD.