Hi,
The guidance shows steps for upgrading from 36.3 to r36.4.
And r36.4.3 is later version of r36.4. If you run $ sudo apt update, the later version will be shown. To stay on r36.4, please have a script like:
OpenGL issue after install nvidia-jetpack via apt-get - #17 by DaneLLL
Compiz high load (180%) - #12 by DaneLLL
To install specific vesion.