Stickers and Stamps
There were many people in early publishing houses that influenced the books' covers; but by far, the folks with the most influence belonged to the Sales Department.
In the top line of covers above, all are first printings. Once a cover had been printed and attached to a book, the company's only options for increasing the cover price were a dust jacket or a sticker. The sticker was obviously the less expensive choice, but it must have taken a pretty substantial number of man-hours to cover each book's price.
Signet D1550 is a really interesting book. First, a Signet sticker raises the price from 50¢ to 60¢. Next, it sports a second sticker making it "Complements of The Committee for the Release Robert Stroud," (aka "The Birdman"). Why would they bump the price for a group that intends to make the books complementary?
The Avon cover (no-number #17) is a later printing. Avon's exec's were obviously a bit narcissistic. The back covers of many books were about the publishing company itself, rather than what the books were about. This stamp may have had to do with promoting the company's name recognition.
The last two examples show how quickly Sales Departments react to market moods. Once again, both the Signets are stated first printings. Jones' earlier works were best sellers, but Signet obviously chose to seize on the opportunity of touting his most recently published work, instead. While the scan fails to show it, the tape they used is translucent, and the printing underneath shows through. The second Pocket Book is a 4th printing. The movie had obviously done well at the box office.
The first image of Pocket Book #455 (1st printing) was contributed by Moe Wadle.