Originally, when I first created The Judas Syndrome cover art in 2009, it was meant to portray the catalyst of the apocalypse in a more painterly style.
Then as the book became a series I realized the cover art wouldn't lend itself to branding three books. So I came up with the stark graphic image in 2010 which lent itself perfectly to using a symbol for each book, yet carrying over the same look and feel.
Then in 2012 I decided I'd make a compilation of all three books into one trilogy and designed the current cover. Then decided I could use this new cover for each of the books and just replace the secondary name and include the original symbols from the 2010 design.
I think the cover has come a long way and feel this may be its last incarnation. The point is, cover design is a tricky business. You don't want to jump into it like I did and keep changing it. I was lucky enough that the books didn't really get selling until I had my second design in place and since it pretty closely resembles the current cover art, I think people will still relate them to the series, but offers them more 'curb appeal'. After all, most people do still judge a book by its cover, and so, as indy authors, we need to step it up a notch and have professional looking cover art for our indy marketed books.