Just because we did the first test in 98, does not mean we didn't have the knowhow before hand. Do you think they all just woke up in 98 and created, designed, validated the nuclear weapon in one year? Read up on the history of the nuke program if you get a chance. It dates back decades. Thy weren't preparing patakhay.
Who would've trusted a claim "I can give you a nuclear bomb technology" without proving to the world with its relevant testing? Without proven test and its results nuclear bomb can be a bomb or a patakha if anyone cares.