I found this when I was looking it up earlier:
the amount of annual snowfall at the Lost Squadron site (near the coast) is much greater than the GISP2 site (far inland near the summit of the ice sheet). The annual snowfall at the Lost Squadron site is around 7 ft per year. So 268 ft of snow in 50 years isn't unusual for that site. The amount of annual snowfall at the GISP2 site is much lower (around 1 ft per year). Using the amount of snowfall accumulation at the Lost Squadron site to infer the rate of snow accumulation at the GISP2 site is wildly inappropriate.