The owner of the company I work at received this postcard in the mail today at the store I manage for him. It really piqued my interest and I had to grab it for my collection.

What makes it strange is that neither my boss or myself know who it is that sent the card and they don't match up to any of our known customers. Stranger is the use of selvedge from a US definitive forever booklet as postage, its acceptance and cancellation.
How would you folks label this if it was in your collection, Cinderella, Freak, Error.
Thanks Scott