A. Put on screw bands firmly so that they are hand tight. If they are applied too tightly, the flat may buckle during processing due to a build up in pressure inside the jar. Air inside the jar needs to be able to escape, which it can't do satisfactorily if the bands are on too tight.
Buckling may also cause tiny pinholes in the flats/lids which you may not be able to see with the naked eye so to speak. If your lids buckle then food should not be stored on the shelf but instead the lids should be removed and replaced with fresh ones then the jars should be reprocessed for the same time required in the beginning for that item of food.
This unfortunately affects the quality of the food as it will have been over processed. Personally I would remove the food from the jars and either pop in the fridge and use with in a few days or I would use what I wanted to and freeze the rest.