There are many authors who use CreateSpace for Amazon distribution of their paperbacks and IngramSpark for paperback distribution everywhere else. There are many good reasons for this covered in many articles, including this really good one from the Alliance of Independent Authors.
However, none of them talk about starting on IngramSpark and then adding CreateSpace later. This is the direction I’m going.
Primary question: Should I use a new ISBN for CreateSpace? Answer: no. Use the same ISBN for both.
This once again points to the recommendation to purchase your own ISBNs from Bowker so that they’re linked to you (as the publishing house).
My next question is about the print quality and formatting differences between the two. I hear that the paper CreateSpace uses is not quite as high quality as IngramSpark. I’m pretty fussy about that. In addition to potentially needing to re-size the cover to support the change in spine width, I might have to increate the price on CreateSpace in order to support higher quality printing. We’ll see.