Device info will only show you the Bootloader the image your running has. It will not show you the boot loader of your sim.
If it states you have bl72 in your device info then with no sticker on the bottom then bl72 is what you have.
If device info says you have say bl69 then the only way to see is flash with a 70 then a 72 image till it wont boot then go back one and that is the sim bl.
Ferret