The copyright date on artwork is not the manufacturing date of the game. The date that is recorded in the database entries is the start of manufacturing, not the start of game development.
The development process of a game can take several months to over a year. Somewhere in that span of time, the artwork is prepared prior to the actual start of manufacturing. And sometimes, the game's development crossed over into the next calendar year.
Additionally, in some cases, production schedules got shuffled around for various reasons, and a game that started development first ends up being actually manufactured in a slot that was a game or two after where it originally would have been.