It used to be 60 to 90 days was all you had for the average mass market paperback. Good sales would trigger re-orders, and sales well above expectations would trigger reprinting of the book. (After all, they only print and ship as many as they expect to sell, based on advance store orders. Again, most of this is determined by the advance--the more the publisher pays, the more the sales force pushes the book, and then there are the afterthought genre books that are largely ordered as lumps--like, "We sold X of that haunted house novel of yours last month so we'll take X of the new one..." where the author truly, truly does not matter. Interchangeable. And quickly, please.)
Of course, my experience is five years out of date and I am sure things have gotten much worse now, because I see only two copies of books by the established authors where I used to see five to ten. Last time I was in a chain store, the book selection had seemingly been cut in half and replaced with beanie babies (and now, I suspect, ebook retail, but I haven't been in a chain store in a couple of years because I have zero reason to go there. Even the ego tug of "Wonder if one of my old books is still stuck in there?" has become boring. Yeah, in the old days we used to move our books around the store so they couldn't find them when the little "Send back" flag came up on the computer.)
If you think of mass market product lines, the entire system is constructed on dynamic rotation of stock. In the 1980's, paperbacks were in every checkout aisle and convenience store and even the trash sold 100,000 copies. Now there really isn't a mass market to speak of. Hardcovers and trade paperbacks get much longer windows, and the returns are different--for mmpb's, stores only need to return the stripped covers for credit. For the rest, they must return the entire books. All done on credit. No bookstore could afford to actually pay wholesale up front. It's ALWAYS been a terrible and tenuous business model, but it was the only way publishers could have a place to sell books.
Kay, yes, I love Amazon because they can do what no one else in the world can do--make you a bestseller in a matter of hours. I am very happy to work with Amazon--but only because I got to negotiate my own deal and didn't have to use an agent. Amazon is now buying entire publishing houses so signing is no longer an automatic--so many other pressures come to bear. While every Amazon title used to be a Kindle Daily Deal at least once, now they have so many that they do them in bundles. Also of particular interest for my genre (and romance writers) is the Dorchester acquisition--they now have hundreds or even thousands of books in my genre that they need to push. Those books will be pushed ahead of me whether I am trad, Zon, or indie, so it really is beyond my control--and falls into the area of "I don't worry about what I can't control." I also suspect they are giving some books--not mine!--preferential algorithm treatment by giving them multipl categories instead of the usual two. I have seen some topping three or more category lists...and that ain't no accident.
Terence, usually the third book is the death knell for the typical author, the point at which you didn't become one of those once-in-a-generation word-of-mouth breakouts and so they move to the next writer. There are only two types of trad writers now--blockbuster bestsellers and those about to be ditched. And, you know, it was ALWAYS the writer's fault, never the publisher's.
And yes, Dalya, it has changed a lot with ebooks, which goes back to my original point--what can trad possibly do that you can't do better (if they aren't going to let you be a bestseller, that is.)