That proves that the one they checked, had the correct firmware. It does not prove that the one from the next batch that you bought did. We are all technical people here we and understand that there isn’t really an easy way to do this that a random non-technical person could actually understand and use.
Isn't the person you're replying to suggesting people can update the firmware to the trusted version via a website? So it doesn't matter if you get one from 'the next batch' - provided you're on top of updating the firmware.