The library on the right goes to the lower level, the library on the left goes to the upper level. But they don't always load from both, especially at park open. The three shafts have different stories in DLP (same creepy protagonist, but different sentences), but I never noticed the drop cycle was different between above and below, I thought they depend on the shaft only.
I know what you're thinking, how can there be two identical libraries in different positions? And six service elevators? It's a space-time continuum paradox, obviously, twilight zone stuff.