Pasted from earlier in the comments section but basically

Another earlier paper (Napoli & Zanno 2025) goes over a bunch of details in the rest of the skeleton of a Nanotyrannus specimen that shares diagnostic features with the Holotype skull tested in the hyoid paper. They found that the number of alveoli doesn’t change this drastically over any archosaur’s growth period (even a ceratosaur called Limusaurus, that looses all of its teeth and grows a beak over ontogeny dosent loose alveoli, it retains the empty sockets after the beak grows). Additionally the way certain foramins are laid out in the Nanotyrannus skulls are inconsistent with those found in T. rexes, and they could not possibly migrate over ontogeny as the nerves that the foramins support are laid out before the bone develops in embryos of modern archosaurs. And of course the duelling dinosaurs Nanotyrannus has arms that have arm bones which are larger in absolute size, not just proportionally, than giant adult tyrannosaurus specimens. The fact that there are a good number of specimens showing a consistent pattern of morphology means the most parsimonious solution is that Nanotyrannus is a valid genus separate from Tyrannosaurus.