Sure, materially speaking, we existed before "ourselves" as individuals but I think that is exactly what "prior existence" refers to; the existence of our identity as entities in the universe. To simplify, if you were to build a Lego fort, the pieces to build it existed long before the fort itself but that doesn't mean the fort existed. Once built, it becomes it's own body, independent of all other material. We are the Lego fort.
"Conservation of energy" theory - energy can never be created or destroyed but only transformed. Part of what we are is energy. Impulses, patterns of energy - something has to put that lego fort together from the pile of legos.
Plus, there are theories that we only perceive time as linear, and that everything that has ever happened or will ever happen is actually happening right now, all simultaneously. Our teeny brains and little bits of consciousness can only perceive things to our ability to do so. We are "cognitively closed" to the real universe so we dwell in a very linear and organized state.
Now pass us that bong, will ya