I've never been a huge fan of subtitles. They always seemed extraneous to me. My opinion has been, if the title is great enough, why do you need more explanation?
So when asked by my editor, in a list of questions, if I was going to have a subtitle for this book, I immediately answered, "No". That was a few months ago...
I have recently made the acquaintance of another Tate author, Elaine Littau, who graciously sent me a long list of "Marketing Tips". One of those tips suggested having a subtitle, especially if your book is part of a series.
So I started thinking, "Should I add one, or not?" I posed the question to my editor (who is awesome, BTW). One issue I had was that I had no idea what I should "name" the series! Another was that same old question, was it really necessary? But she was completely on board, and had actually been thinking we needed to add one as well.
Now we are simply waiting for my cover designer to get back in town, to find out if it's too late to add "Book One of the Summers Saga" to the cover.
I'll keep you posted:)