which SEC regulation regarding insider trading stipulates "of companies tell anyone, they must tell everyone"?

Answer: Regulation Fair Disclosure (Reg FD)

Explanation: Passed by the Securities and Exchange Commission, the aim of this rule is to prevent public companies from releasing selective disclosure to a limited group of people. Reg FD goes on to state that when these public companies release info of material value to certain professionals and shareholders, then they are obligated to publicly disclosed this information as well. It is important to note that this regulation doesn't necessary require info to be disclosed to all individuals outside the corporation, but merely disclosure to professionals within the securities market.