In 1989 the USPS started selling Postal Cards with a picture on the back side. These cards were sold at premium prices, well above face value. These issues were UX143, 144, 147, 151, 163 and 168.
In 1994 the USPS kicked into high gear, issuing Scott #UX178-97, the Legends of the West. These cards had a face value of $3.80 and were sold to the public for $7.95. For future issues, that premium over face value would get much higher. The worst of them was Scott #264-79, the Endangered Species; the face value was $3.00, and the issue cost was $11.95....roughly 4 x face! In addition, there would be no more "single" issues; now, everything would be issued in packs, booklets, and sheets of 10 or20.
These packs/books/sheets were issued to the public in SHRINK WRAP and carried the inscription "Package not Suitable for Philatelic Archiving". Translation: The wrap will eventually twist the cards and/or mash the corners. These cards were intended to be mounted in an album and should NOT be saved in their original shrink-wrap packaging.
Cards which were issued in BOOKS of 10 or 20 can survive sitting on a shelf for a long time; the thickness of these books protects them well from the squeezing effects of the shrink wrap.
Cards which were issued in SHEETS, however, are often found with slightly warped corners. Mercifully, the USPS discontinued these sheet-issued cards and returned to the "booklet" format.
Your satisfaction is important to me....which is why I'm a careful buyer, and I'll do my best to stock and sell only the highest quality cards. Still, you MAY, on OCCASION, receive a card which is just a smidge less than perfect. This might occur on the following sheet-issued cards: Scott #279, 300, 317-36, 357-60, 377-80, 382-5, 386-9 and 401-4, as well as the later "Nature of America" series.