Cuba Cinderella

So apparently, the design shown in your cinderella was used to publicize a contest in 1950 for submitting designs to be used in the actual postage stamps that were released in 1951. The contest, and announcement of winners, can be seen in this link: Las Emisiones de Sellos y Medallas. (Brush up on your Spanish, or use a translator like Google translate -- and get some chuckles while you are at it)

Unfortunately, I did not see any actual mention of the cinderella you have, even though the basic design was used in the announcement flyer.

Sorry. k doesn't collect cinderellas, so this is well outside what I know.