Ultra Mek Inc v Man Wah (USA) Inc

The concept of corporate legal separateness has long been a fortress protecting affiliated business entities such as parents, subsidiaries, and sister companies from various kinds of liability and litigation. However, how much protection does such legal separateness offer the information that corporations gather and store when faced with vehicles of written discovery such as interrogatory requests or requests for production? In other words, if an opposing party requests information or documents from a party that requires that party to seek information or documents from an affiliated non-party entity, is the party then required to seek the requested information or documents from its affiliated non-party entities?