to be perfectly safe, the lids aren't to be re-used for food that is going to be processed and stored unrefrigerated. i reuse them for stuff i'm storing in the refrigerator or freezing.
there is a "new" old system out there this year: reusable plastic white lids with detached rubber rings that are one use. the rubber rings is a reversion back to the rubber rings of the glass jar lids with the wire bale. the rubber on either the old style Ball and Kerr lids is what does the actual sealing once it it is heated and stays sealed because of the vacuum created by the processing. the rubber rings on the detachable system does the same