I'm very new to canning, so maybe some of you could help me out: I canned 4 jars of garden salsa in early January. Ate 2 jars, gave 1 away (they said it was great), and took out the last one today. Unfortunately, the center seal had popped up. I took out my canning instructions which said 'don't mess with it, throw it away', so I did. I read the possible reasons why this could happen, and it said several: lip not clean enough, jar with tiny crack/chip on lid, etc.
I'm not sure... Do I use this same jar again? I didnt' feel any cracks. What should I do?