A non-disclosure agreement cannot supersede the SEC's rules. A partnership must be disclosed within 4 days of the signed agreement. Note the "signed" agreement -- they don't have to disclose it while they are still negotiating, because it's not a done deal, so there is nothing that is a material event -- yet.

"There's many a slip twixt cup and lip" applies here. The SEC would not want to require people to disclose every time they're negotiating because that would really cause stock gyrations, and possibly needlessly so if an agreement were not reached after all.