Specifications saved for an ICAO Type will be used for all aircraft sharing the same type, Subfleet definitions will apply to all members of that fleet, finally aircraft based definitions is also possible (but not advised).
(1) : Most important fields for proper SimBrief flight planning according to the addon being used.
(2) : When used all three fields must be defined otherwise it will not be used for SimBrief planning.
Order of loading/selection during usage is simple as Aircraft > SubFleet > ICAO Type