The magazines I receive at home are usually labeled weeks
or even months in the future. Could they have been
delivered by a time travelling postman? And if so, why
didn't he bother bring me the winning lottery numbers while
he was at it?

Confusing as it may seem, the date on most magazines isn't
meant to represent when it was published. Instead, it's the
literary equivalent of an expiration date and it serves two
purposes. First, it gives the consumer the feeling that
they're getting the latest news, even if the magazine is
actually a few days old. Second, it helps retailers know
when to remove the old magazines from the shelf. Once a
magazine's date matches the real date, it's probably time
to display a new edition, also dated way in the future.