They are right. "Last" doesn't take determiner when means 'past from now'.
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SnappyIn my understanding, "the" is not required before the word "last" when we refer to things that happened last week, month, year, etc.The showing of the company's sales figures did not happen last year. You are only using "of last year" to indicate which sales figures you are talking about. Therefore you may use the
tarirotariBecause in your sentence (Could you show me last year's sales figures for the company?) the showing of the company's figures did not happen last year either, but I think it wouldn't be right to use "the".I agree that it wouldn't be right to use "the" in that sentence.