How do we know they're right this time, rather than in 2005 when they said the opposite?

I guess the NIE gets to have its cake and eat it too.

"2007 National Intelligence Estimate. This year's NIE does indeed reverse the NIE's 2005 finding "that Iran currently is determined to develop nuclear weapons." The new conclusion: Iran's "halt" of its dedicated nuclear weapons program began in fall 2003."By Bennett Ramberg
from the December 6, 2007