I recently ran a free (KU) promo on the most recent book in a series and advertised via Fussy Librarian. i was quite surprised to find many of the purchases and page reads were for the earlier series books. I hardly do any promotion normally, and I very often forget about the KU free days, so that probably helped!   It wasn't exactly brilliant by most people's standards, but I got 13,700 page reads which is about 13,000 more than usual!
(I do also still have some permafrees in my longest series, but I see them as a kind of reward to readers for slogging through the 28 books!)

Complete agreement with Al. I have three books that are "permafree," for which I have run numerous marketing efforts.

With over 4k "sold," one novella is constantly in the top twenty of several subcategories.

After extensive research, at least six strategies failed. Confirmed follow-on sales? A guess of ten in two years is a high number.

When "wide" failed, I targeted the audience to a series of narrow bands that I thought would be inclined to make a follow-on purchase?more failure.

Here's my theory: There has always been a challenge in capturing disposable income. 'Zon and others pushed the proliferation of free reading material, which has exacerbated the expectations of the casual reader. The audience looking for "a freebie" is now the audience looking for the next freebie.

A compelling story that draws the reader to the next in the series has always been the ball we push higher up the hill. Now the hill is steeper, the push longer, and the summit further into the distant sky.

Yes, Sisyphus, this is an informed opinion.

R.C.

So many authors do free and I've seen many recommendations, particularly for wide authors like me, on how it's sold books. I want to share my experience over the past 6 months. I'll start by saying everyone's different. Market your way. Just because it didn't work for me, doesn't mean it won't work for you. According to the writing forums, the strategy works for most writers wide.

So, regarding permafree, I'm done with it. I set an initial book as free for one a bestselling series. I gave away around 6k copies, 2000 over the last six months without advertising. The free book ranked on Amazon in the top 10 free under occult. It sold "free" well.

Results. I lost hundreds of dollars in advertising. All advertising led to people grabbing the freebie and not buying. Unlike the purchased, most didn't buy the next in series (because the next cost money? dunno). The sales of the actual books on sales plummeted. Before someone thinks it's the books, the same books are on boxed sets. The boxed set sales were unaffected and I was able to move ads to them--just not enough.

So I've got a book here ranking in top 10 free on Amazon with a successful selling series with links in the backmatter and the series sales dropped. And everyone on every writer forum should had said I'd be expecting great results. Why didn't all the magic work?...  It goes to show that you have to do what works for you.

It's like BookBub ads. I owe my past few years of sales to my success with them. But so many authors talk about how they can't sell with BookBub.

Anyway, I thought I'd share my experience. It goes against all the advice you hear on writing forums. Sorry, no more freebies from me.

I'll add two more things. Email promotions for setting a book free still works for me. Don't know why, but on impulse, buyers buy. Finally, I thought a free book would lead to audiobook sales over the same book. It did, but too measly to make it worth it. My other audiobooks in series fare much better.

My merger has just been completed.
It looks to me like my D2D print books are a separate listing to my Smashwords eBooks for each publication because of the ISBNs. I am happy to wait and see, because my D2D print books are still selling at least one a month just fine.

They claimed to be starting on my merge months ago, but it certainly is taking a while. I have most of my stuff on Smashwords under my pen-name, and a handful of things on D2D under my real name. I can't even remember why I bothered to set up the D2D account in the first place. I would have unpublished everything from it if I'd know about the merger but by the time I thought of it I was apparently too late.