Due to the adult having a significantly larger hitbox, upon loading my world up again, my tremorsaurus with curse of immaturity suffocated until I swapped its collar out for another one and then gave it the curse of immaturity one again, as it was seemingly using its adult hitbox.

I'm guessing this may have always been a problem, but was never noticed due to most tameable mobs not being very big.

Note: I know it's suffocation because that's what the death message said the time it died before I respawned and did the collar swapping.

Update:

The nametag now shows up where it would if it were an adult. Before the incident, the nametag just showed above its head.

Its collission box also seems to be that of an adult tremorsaurus now.