When you provide a positive creep value, the centerfold is not adjusted, but the pages on the outer sheets move away from the spine.
The creep increment is calculated by dividing the specified creep value by the total number of sheets minus one. The term sheet represents two printer spreads: the front of the sheet and the back of the sheet. InDesign considers the “cover” of the final piece to be the outermost printer spread, while the “centerfold” is considered to be the innermost printer spread.
