Looking at GPA, it is worth more in grade than TTA 27 across the board, and has gained steadily the past 2-3 years in 6.0 and lower grades (while TTA 27 is trending down). The big gap ups were 2009 with the movie announcement when copies across the board did a 2-3X in months (the good old days when dealers were slower to update prices online ), and again in 2014/15 when SA keys popped again across the board. It is all over the map in higher grades as the pool of buyers is smaller, but in 6.0 and under the book is doing okay.