What is the relevance of Implement dock date and due date in constrained planning?

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What is the relevance of implement dock date and due date for a buy planned order in constrained planning? How is the requested ship date of the corresponding Purchase Requisition derived from the Planned Order?

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What is the relevance of implement dock date and due date for a buy planned order in constrained planning? How is the requested ship date of the corresponding Purchase Requisition derived from the Planned Order?

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