Here's a quick post to answer a question my sister had: How can you tell the difference between used and new canning lids? There are a few ways to tell. First, the new ones are in a box and second, the used ones have the date sharpied on them :) However, if you used lids on freezer jam, they aren't in the box and have a date sharpied on them, but they are still not USED. And sometimes new lids get mixed in with old lids in the sack/box/wherever you keep your canning goods. And sometimes you might not have marked the lids. So here's a better method. Turn them over and look at the gummy stuff around the rim. If it's smooth like this one, it has not been sealed and is good to use to seal a jar.
If it has a deep jar rim indentation in the gummy stuff, like this one, it has already been sealed and cannot be used again.Sometimes if the lid has been on a jar like for freezer jam, or if you store your empty jar with a lid on it and the gummy side has been against the jar rim, it will have a slight indentation in the gummy stuff, but it's still good to use. It will not be as deep an indentation as a lid that has sealed. Hope that helps!