In fact, before passing 1996 new immigration reform law, any one, even B2 parents got SSN easily, and communication between SSA and INS (now USCIS) only started after that. So if a person got an SSN early 1990s, then returned to USA using a new passport. He/she might be successful in getting a new SSN without been detected. However, it's not legal to have a second SSN without SSA approval of your having two SSNs.