We'll have a couple to fail every couple of canner loads. If we do 2 loads in a row, I'll usually re-lid the fails.
Most of our fails I can find debree? (come on spellck) under a lid. So either over fill or over cooked. I've been preaching we are over pressuring

but it hasn't sunk in yet. I finally put a gauge on the canner along with the rattler. She's starting to see...
Good on lids here also. I've shopped/bought the deals for several years now. Can probably go 5-6 years without any new purchases.
I also have some older Kerr's that when opened, part of the seal will stay on the jar and has to be scraped off. Normally that doesn't happen. I'm still going to use them up.
I've been cruising ebay this am. Most all lid sales now are a rip.

Fixing to go ck Amazon. Used to be some deals there.