The lawyer's advice is following the line of what would be easiest for her, not necessarily what would be best for your bank. Regardless, if you have proof of death, I see no privacy implications to answering the question "yes" or "no." As for inconveniencing people by requiring the letters before you give them any other details, the individual is not the personal representative unless he or she already has the letters. Actually, if he or she does not have the letters, they should not be asking the question.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.