The General Electric Corporation was America's largest Television dealer during the 1950s. They sold millions of TV sets, and maintained a network of thousands of "Authorized Dealers".
Those dealers had it good; the various tubes, as well as other parts which were inside the set weren't designed to last forever.
G.E. developed a promotional program to make sure that TV set owners were pointed in the right direction when the inevitable came to pass and the TV sets needed repair. They printed ads, including the name, address, and phone number of the dealer, on the back of the then-current 2c Postal Cards, the UX38. The cards had holes drilled into them (so they could be placed around the Power Cord of the TV set) and were mailed, in bulk, to the dealers.... who then either mailed them, or handed them out, to the TV set owners.
In 1958, the rate for the Postal Card increased from 2c to 3c and G.E. found themselves sitting on nearly a million cards which had been prepared for distribution....much like the one above. And so G.E. asked the USPOD to re-value 750,000 cards, thus creating the scarce UX47 variety.
And this would be the end of it... except that Postal Stationery Collectors and Dealers soon realized that there were several different types of ads in existence. To this day, we're not certain how many different ads exist. The UPSS Postal Card Catalog lists 16 different varieties of UX47. There could be more.
It was also discovered that NOT ALL the UX38s were re-valued. These ads also exist on UN-re-valued UX38s. Again, nobody is certain how many different varieties exist.