If that were true, then you would be presented at device power up with the option to boot from one version or the other.
Is that what one sees?
It is atypical for these smaller electronic devices to provide such an option. What may be more typical is the ability to hold two (2) operating
software versions in memory during an upgrade procedure. This is a fail safe option allowing the device to recover (and boot from the earlier version)
in the event of some failure during a software upgrade process. The last step in an upgrade is to update the device's boot address to the
newer software version. If that step is for whatever reason not reached, the device boot address of the older operating software version is
retained - and the device is not "bricked".