Such material defiles the integrity of ones collection and is best avoided. Ludwig Mies van der Rohe was right - often less is more. At the very least, the issuing country must be a member of the UPU - the universal postal union. As a secondary requirement, the stamp must primarily have been issued for postage use. Stanley Gibbons, the highly respected English philatelic house, goes some way in making this distinction in their excellent catalogues, by placing 'cinderella' issues into special Appendix listings.
Many people enjoy collecting cinderellas.
However, such material does not belong in a stamp catalogue, and is not listed here. This is a somewhat contentious issue. However, if that stamp also had draught pieces on the board, then it would generally not be considered a chess stamp. Further, note that the chess motif must be found on the stamp itself. This will be the final beta release.