Project Gunrunner has been in operation since 2006. It is well known; but the Gunrunner name just refers to a broad overall program to interdict gun trafficking to Mexico. Fast and Furious aka Gunwalker is part of the Gunrunner program; but they are not the same thing. Some of the Gunrunner projects may have been perfectly legit, though it appears the Phoenix and Tampa projects were not.
So while Holder probably knows about Gunrunner, it doesn't prove he knows about the details of Fast and Furious or the latest story about the Tampa office walking and losing guns to Central America.