(I intended to include this in my previous post. Better late than never?)
First, note that once you click Approve Proof, it is no longer possible to change the publication date.
As mentioned in my previous post, after you enter the title information, much time can pass before you approve your proof (from making revisions). So if you enter the publication date as ‘today’ when you enter the title information, by the time you approve your proof, this date can be a few weeks old. The problem with this is that you would then have very little time in the ‘Last 30 Days’ section.
At CreateSpace, when you enter the title information, if you click on the ‘What’s This?’ link, you’ll see that you don’t actually have to enter any date at all. Just leave this field blank and CreateSpace will automatically set the publication date to the day when you first click the Approve Proof button. This gives you approximately 30 days on the ‘Last 30 Days’ list (since it may take a day or more for your book to show up at Amazon).
If you didn’t know this and entered an actual date in the title information, when you go to the title section, you may find that everything appears to be ‘locked.’ If so, contact CreateSpace and explain the situation. Make it clear that you have not clicked Approve Proof (even in the past) for this title, and ask CreateSpace if they could please reset the date for you.