Letter sent in 1945 just now returned to sender

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The San Francisco Chronicle newspaper received this returned mail last week. The USPS label says: “Not deliverable as addressed. Unable to forward.” No surprise, considering the letter was mailed in 1945 and the intended recipient had moved from that address before 1970 and has since died. The reporter who mailed the letter is also long dead. "How did a 68-year-old letter get delivered to the Chronicle?"