The question now is whether there is any important, structural difference between propositional memory that begins as event memory of the event that the proposition is about and propositional memory that doesn't significantly involve event memory.  For example, my memory that my driveway was icy last Christmas is propositional, yet it is based on my experience of the event in question.  My memory belief that Abraham Lincoln was shot in Ford's Theatre is not based on any such event (although, of course, for virtually any non-innate belief, there will be some event that leads to its formation). 