Are RAP (Redundant Acronym Phrases) grammatically wrong?

Two examples are PIN number" (the "N" in PIN stands for "number") and "ATM machine" (the "M" in ATM stands for "machine? I know that it will be redundant if "PIN" is extracted to Personal Identification Number + Number. But can anyone explain it to me well. show more Two examples are PIN number" (the "N" in PIN stands for "number") and "ATM machine" (the "M" in ATM stands for "machine? I know that it will be redundant if "PIN" is extracted to Personal Identification Number + Number.

But can anyone explain it to me well.
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