I have speculated before that Coupon's are often in worse condition than other cards due to their packaging. While most cards of the era were packaged in slide and shell cigarette packs (cardboard packs with an outer shell and inner slide), Coupon utilized a soft pack configuration. See my website below for an image of the pack:
http://www.baseballandtobacco.com/t213.htm
Because the pack was not stiff, the card inside was not that well protected (or so I assume).