Right now both the self and the manual enrol plugins lead to the creation of ras with empty component and itemid.
While it may be considered a border case to have both plugins enabled in the same course, it's not impossible, so at some point we aren't going to know which enrol plugin belongs to a given ra in a deterministic way.
So the idea is to start using the component and itemid for self enrol instances for better differentiation in the future.
Speaking generally, any enrol plugin (core or 3rd part) but "manual" should be always using component + itemid when creating ras. As simple as that.