Thawed vs unthawed isn't a bool. You're really interested in the long-term safety of the food, and that starts to decrease as temperatures start to increase.
-18C/0F is the point at which most pathogens are forced to hibernate and bacterial cultures stop growing. But they don't die, and they'll start to revive at higher temperatures - which means they'll begin to spread if there's a regular thaw/freeze cycle, even in a freezer that spends some of its time at -18C/0F.
-18C/0F is the point at which most pathogens are forced to hibernate and bacterial cultures stop growing. But they don't die, and they'll start to revive at higher temperatures - which means they'll begin to spread if there's a regular thaw/freeze cycle, even in a freezer that spends some of its time at -18C/0F.