1974 Proof Sheets - Why are the First Nine Cards Commonly Cracked?

I looked at the 1974 proof sheets from a 2015 auction to see if the 1974 cards were laid out in such a way that the first nine cards would end up being cracked.  All three proof sheets do have these cards across the top row.  Check it out in the picture below.

So, would it be possible that the top cards on these sheets cracked more frequently than the others?  What would cause that?  Or is it the nine-pocket pages with the cards on page one having issues?  

Someone help.