Leibniz and Krikpe on Trans-World Identity

For Leibniz, even though whatever happens to an individual substance is certain to happen (since everything is included in its notion), if the contrary were to occur, that would not be impossible in itself, but only ex hypothesi, given the actual sequence of events.1 Of the infinitely many things whose opposites in themselves do not imply a contradiction (i.e., of infinitely many possible things), the one that will be true has more reason or is more perfect; God chooses the most perfect of all series of events and things (i.e., worlds) to bring to reality. Therefore, not all possibles attain existence, and there are infinitely many possible things which do not, have not, and will not exist. Leibniz saw this as his definitive strike against necessitarianism: if other things are possible, then what actually exists is not absolutely necessary.2 If, according to the Leibnizian PIN principle, the perfect notion of a thing contains all of its past, present, and future predicates, then how can the epistemological and logical distinction between necessary and contingent propositions account for the intuitive fact that, for example, Julius Caesar might have not crossed the Rubicon? In other words, how are alternative scenarios even intelligible? God chooses not between possible things or scattered events, but between complete series of things and events, from the beginning of time to eternity, so the complete notio