The sentences that contain an example of contested usage are:
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"The postman needs to know who this letter is addressed to so it can be delivered." (The contested usage here is the preposition "to," as traditional grammar rules suggest it should be "to whom" instead of "who.")
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"The chair for the chair of the board of directors is at the head of the board table." (The word "chair" can lead to confusion as it is used to reference both a member (chairperson) and a piece of furniture, leading to contested usage in terms of clarity and appropriateness.)
Please confirm that these interpretations align with your understanding of the sentences in question.