What Krsna says is all perfect and certain and is applicable to the past, present and future. Nor is there any uncertainty for one who knows exactly what Krsna says. The Krsna consciousness movement is based on Bhagavad-gita as it is, as spoken by Lord Krsna, and for those who are engaged in this movement, there is no question of uncertainty.

From Srila Prabhupada's purport to SB 4.24.42