why msm kernel has both 3.18 and 4.4 in 8.1.0 oreo releases

[laos...@gmail.com]

for example, https://android.googlesource.com/kernel/msm/+/android-8.1.0_r0.78/Makefile has 4.4 kernel while https://android.googlesource.com/kernel/msm/+/android-8.1.0_r0.117/Makefile has 3.18.73 kernel, so the newer minor release 117 has much older kernel than a previous minor release r78? am I missing something?