RockPiS RK3308 unique ID

Hi all,
I’m testing Rock Pi S running Ubuntu 18.04.
Does anyone know if the Serial in /proc/cpuinfo (last line) could be used as a unique ID? My board shows: “Serial : 0698d618fbe56275”.
I wonder where this 64bit number comes from. Datasheet has no information on chip unique ID.
I also observe that eth0 MAC seems to be unique, while p2p0 MAC changes every time wifi is switched on and wlan0 MAC changes every boot. Is this correct?
Thanks all,