It’s well known that collectible toys are worth more when they’re still in the package. In 1977, the package was all some Star Wars toy seekers could get.

In the mid-’70s, Mego Toys was the a big player in action figure—essentially dolls marketed to boys modeled after characters from movies and TV. Big sellers for Mego included Star Trek toys, Starsky and Hutch toys, and dolls based on the band members of Kiss. Mego Toys went defunct in 1983—if only it hadn’t rejected the right to make Star Wars toys. Yes, the company didn’t see much commercial value in the movie when it was approached by Star Wars producers in 1976. The movies, and the toys, went on to each generate more than $1 billion.

Instead, the makers of Star Wars signed up the relatively small toy company Kenner to produce items based on the movie. It would eventually make Kenner one of the biggest toy companies in the world, but in 1976-77, the company was completely surprised by the film’s popularity. Star Wars would become a cultural phenomenon in the summer of the 1977, and the highest-grossing movie of all time. As such, Kenner was ill-prepared for demand, and initially wasn’t even going to produce action figures, but instead low-cost, easy to manufacture things like puzzles and coloring books. But that’s not what the kids wanted in 1977: They wanted action figures.

Kenner went to work creating action figures based on Luke Skywalker, Darth Vader, and all the others. It involved design, sculpting, product testing, mold-making, and then mass production of millions of individual, 4″ tall dolls. But there was one problem: There was no way the action figures were going to be ready by the Christmas 1977 shopping season. Amazingly, Kenner had one option, and they went with it, and it worked. It sold empty boxes.

Hundreds of thousands of kids opened their presents on Christmas morning and expecting a set of 12 Star Wars dolls instead received an “.” A diorama featuring drawings of the movie’s characters and other scenes, it included a certificate that kids would mail in, and they’d receive, in a few months, the Star Wars toys their parents had already paid for. It wasn’t a toy, but a promise that a toy would be sent very soon.

This oddity is now among the rarest of all Star Wars merchandise. Why? Because most, if not all, of the kids who got their Early Bird Certificate sent it in right away, where they were received and filed away by Kenner.