Although, Microsoft release license guidelines for each & every SQL server version. But there are more complex scenarios for licensing then we think.
Best person to answer your all queries over licensing is MICROSOFT itself.
You can call Microsoft Licensing at 1-800-426-9400, Monday to Friday, 6:00 A.M. to 6:00 P.M. (Pacific Time) to speak directly to a Microsoft licensing specialist.
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Reference : Rohit Garg (http://mssqlfun.com/)