I'm sure you're not an engineer now lol
Do you think the physics of nukes is widely shared, accurately? That no one spread a few incorrect formulas to reduce proliferation? If you can't test along the way, you need to know exactly how it works.
Without help or the ability to experiment, they're doing it on hard mode. These are worse conditions with less funding... The only advantage they have is knowing for sure it's possible
And as far as MAD... Do you think Israel has ever been inspected? Of course not. Because the game has changed
Optics are more important than reality. Right now, the intelligence community doesn't think they're close to a bomb. If that opinion were reversed, that's just as good as having a bomb