Freezer burn (assuming that's what you are worried about) is a condition in which frozen food has been exposed to air. When food is frozen, water molecules in the food turn into ice crystals. These ice crystals then migrate to the surface of the food, which is why you often see layers of ice crystals on your frozen foods. Dehydration of the food then occurs because water is effectively being pulled out of the food. I would not think that a vapor lock in the middle of the bag would mean the fish would freezer burn (or otherwise ruin) at all, because the vapor lock would still be surrounded by some good ice and the bag itself that would help insulate that area and tend to prevent the air circulation (heat exchange) that would cause dehydration and freezer burn.
I wouldn't worry much at all about it... but would suggest that you try to use up these packages within a month or maybe 5 or 6 weeks.