I don’t know how significant any of this is, but I noticed that when Evil Queen Regina goes to the Hatter’s home her necklace is the round metal piece, which is what she wore when first seeking out the Huntsman. The door to the vault with her hearts has the same pattern as the Queen of Hearts vault in her labyrinth, and it’s the same pattern to Mayor Regina’s Father’s crypt. The wall lockers holding the cases for the EQ’s hearts, Mayor Regina’s hearts, and the Queen of Hearts’ vault are all labeled with, ‘XC’.
Are the heart boxes reserved for specific people? The box EQ Regina had for Snow White’s heart is different from the box she used for the Huntsman.