Why is the communication management plan not an input to plan stakeholder management? Wouldn't you often appoint specific people to communicate with specific stakeholders ? It happens at my work all the time...issues have to go through the proper channels, and often communication with stakeholders is reserved for whomever is closer to them in the channel.
regarding your question, the first input to stakeholder management is the well known commonly used input "Project management plan" which by definition includes all other subsidiary plans including the communication management plan. hope this clears your confusion.
reference: check section 220.127.116.11 from the latest PMBOK guide version. It describes why the Project management plan is an input to the stakeholder management, one of them is "Need and techniques for communication among stakeholders".
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