I always look at every plug when verifying the gap. I’ve seen all kinds of stuff you wouldn’t see if you didn’t look right at them. I think it was a set of Autolites, but it may have been Champions that out of a set of 8, three had a hairline fracture down the porcelain. Have no idea how that happened but I was down to one of the last plugs and found it. Went back though them all and found 3 more, but I needed my magnifyer to see those. You find all kinds of crap, like the ground wire isn’t welded on correctly. I’ve seen them fall off. Or the ground wire isn’t parallel to the center wire. Just drives me nuts.