I have one set of people saying that a page did not pre-date a Facebook post, and another set of people saying that they did.
As best as I understand it, it is not possible to pre-date a Facebook post without a little clock icon showing up.
When you hover your mouse over the clock, it shows you the original (actual) date that the post was created.
Changing the date is only possible on the desktop (both on personal and fan pages). However, on a mobile device you can still see this little clock. Although you cannot click or hover over it, it at least gives the user an indication that the post was moved.
Here is a post that does not have a clock icon. (It's on a "page," not a "group," meaning it's impossible to be anything but public).
Is there anyway to hack Facebook, such that you can change the date of (or simply create) a post back in time but suppressing the clock icon? If this is possible, then it essentially gives people a way to create fraudulent posts. And in this particular case, determining if this is possible turns out to be very important.