With 12 unrestored copies in the census, a ridiculous number for a book that doesn't even sell for $25 in Good, it's obvious the Gerber number is wrong on this one. I'd guess the main reason why there are twelve graded copies is that people going strictly by Gerber send this in to be slabbed far more frequently than the underlying value would dictate.
A few rules on how to use Gerber in the age of the Internet:
Check the census, Heritage, and Metro to confirm scarcity
Compare that data to the value of the book (higher value books will be slabbed more frequently)
If a Gerber "8" sells for over $100 in Good and has 3 or fewer unrestored copies in the census, then it's truly scarce. If it sells for less than $100 in Good then the census data could well be skewed because the value proposition of getting it slabbed falls (although just the Gerber "8" designation can be enough to ramp up submissions as the Warrior Comics shows).
Creating a market value + census/Heritage/Metro matrix in a spreadsheet will also show a number of Gerber 5, 6, and 7's that are actually exceptionally scarce.