If it was published in 1967, it is probably a book club edition. Folks, this was the same dinky black cover pbk that has been floating around since the 70s, with different ads in the back with each printing. If you think I'm joking, I'm not, someone actually tried to sell this item through ebay. There were no bidders. What people forget is that HST was not taken very seriously as a writer at the time, and not many people thought to put away their books for safekeeping.
Chances are, many copies ended up like the waterstained one, or even worse.
When the FLLV movie came out, book prices jumped even higher and more editions came out on the market. Book prices are subjects to the whims of the public, and as HST gets older , book prices can only go higher. You can use these criteria to judge a book that you are considering buying or selling. I always make construction paper covers for mine, and I keep the mags in a Ziploc bag with a piece of acid free cardboard. Bumped corners are also common on paperbacks, as well as spine stress.