That chart says nothing about sample size between the two events.
The chart also says nothing about the ages of the t-shirt requesters, or if people decided to get larger ones the second time around to offset shrinkage they were not aware would happen with their previous choice.
also the same people who were 18 and 20 in 99 are about 30 in 08. and married, driving minivans, easting home cooked, chasing less/no tail