Re: If your not on the list, you're not getting in
I believe India never signed the Nuclear Non Proliferation Treaty. So they were never bound not to develop nuclear weapons. It only applies to you if you sign it. Although as I understand it signatories aren't supposed to cooperate on civillian nuclear shinies with non-signees.
North Korea did sign the NNPT. And then developed nukes anyway. They also specifically agreed to halt their illegal development of nukes during the 90s famine, in exchange for aid. A deal they also broke. They haven't been invaded, and no evidence has been manufactured. They've tested nukes, so we know.
Pakistan and Israel also didn't sign up.
The point about signing a deal then breaking it is that your're automatically going to be less trusted. So the reason everyone joined sanctions on Iran is that they breached the treaty by secretly developing nukes - and then got caught. After years of sanctions, a deal has been agreed.
Iraq did have a nuclear program by the way. The UN demolished it in the mid 90s. I think the reason it was deemed legal to invade in 2003 was that they were still in breach of the ceasefire agreement from 1991 - which they'd never complied with despite ten years of inspections and sanctions.