Harry Potter and the Cursed Child is not a play. It's a rehearsal script. Something hardbound but not a literary work like, say...oh I don't know...The Cherry Orchard. The rehearsal script is a cash grab, but it's also the foundation for (by what I've read on the InterWebz, anyway) a fantastical stage production. Plot holes be damned! Who cares if the world-building and rules of magic (ahem -- Time-Turners -- ahem) in the seven Harry Potter books are tossed in the ash can? Rowling's wizarding world in all its iterations is great fun. Truthfully, though? The Potter story arc could have been wrapped up in four books. House-Elf history and wand lore is just so much filler that distracts and detracts from Harry's journey. HP&TCC in written form is equally unnecessary, but I'm sure the theatrical performance is a special kind of magic all its own.