So I've discovered Apple's mystical implementation of hard linking with the new Photos app library and the old iPhoto library. Although Finder reports that both take up a significant and similar number of GBs on the disk space, they apparently are pointing to the same data on my disk, so data hasn't been duplicated.
Question is, how can I verify this? If I check the size of the parent folder, it's also reporting double GB. I imagine I can check all the folders at the root level and find that the total adds up to more than what I have based on free space... but that doesn't actually pinpoint what files are hard linking.