I saved hundreds of poorly plated cents found from 1998 to 2001. They had many blisters, lines and spots that all looked so random. I came across these 2 that I must have set aside back then.
First has a weak line through the date from the A to the left leaf, with a small blister by the 1, and several tiny bumps on the leaf.
Then there is his muscular, bigger brother, which runs from the rim below the A and to the 1 of 1 CENT. The small bumps on the leaf also bulked-up.
Seems to be a progressive occurrence, not random.