Originally the Niro EV was supposed to get NCM 811's, a more advanced battery chemistry from SK Innovation over the NCM 622 used in Kona. SK reportedly had delays in 2018 but were supposed to go into production of the 811's in 2019... did they make it to the 2019 vehicles? This might explain why we are seeing such good range for the pack. We already speculate the actual pack is larger than the 64kW since it has been reported DCFC charging current doesn't taper as it gets to 100%, so there is probably a buffer in the top-end of charge. I am hereby starting the conspiracy theory now that the cars today actually have 811's (hence the small number of vehicles built & sold due to supply of 811's) and its a secret to be unveiled as a larger capacity pack in next model-year vehicles.
https://pushevs.com/2018/05/09/most-advanced-battery-cells/
https://pushevs.com/2018/05/09/most-advanced-battery-cells/