From my headcanons, Jack was on North’s naughty list not because he was number one but because his name managed to stay in the book for over a hundred years. The record North mentions is the that Jack’s name was on the list the longest, not because Jack was the naughtiness. He just managed to remain steadily naughty for a long time.
It’s probably gone now.
Probably. North doesn’t control his book of naughty and nice kids, it sorta works on it’s own magic.