Yep, you're unlikely to see the kernel change versions. For i.MX devices, they're based on NXP's original tree, which is itself based on specific LTS releases.
(e.g., Mk. 7 kernels are probably based on
https://source.codeaurora.org/extern....1.15_1.0.0_ga or
https://source.codeaurora.org/extern....1.15_2.0.0_ga)
To my knowledge, the only device I've ever seen update a kernel patchlevel was the reMarkable, when they jumped from 4.1 to 4.9 on the rM1.
Close second would be Kindles, where lab126 has been working fairly actively on the kernels of their released devices in the past.