Most likely they meant unlock, but in the off chance... I've used galleries as a milestone markers. When I see I've done the last scene in the gallery I know I'm somewhat close to the end the update/game. Then make a few saves before the end in case the next update bonks last save, I'll have something close.
I know the Unlock code in the OP (under cheat code section) gives you access to unlock gallery button. If you click the unlock, it opens the gallery up and changes button to lock to relock it later. Not sure if it relocks all or just the one you never saw. Seems easiest solution is unlock/lock all.