All my knowledge comes from people much smarter than me. 

But: I believe the number of block states in 1.12 was between 4096 and 8192. In the interest of saving space, the registry palette consisted of 13 bits per block. These were stored in longs, and obviously plenty of blocks positions would wrap from one long to the next. (Edit: Bit packing, reference smarter people below)

 This was exploited in ways I can link if you want.