So how did the 'due date' meaning arise? Was it related in some way to the prison line?
Edit: according to wiktionary, in the 20th century it was used in the printing industry for a line on the bed of a press beyond which text wouldn't print, then by analogy as a time limit after which a newspaper story wouldn't make it into the paper. It's not clear if this sense was inspired by the Civil War prison dead lines, or made up independently.
Edit: according to wiktionary, in the 20th century it was used in the printing industry for a line on the bed of a press beyond which text wouldn't print, then by analogy as a time limit after which a newspaper story wouldn't make it into the paper. It's not clear if this sense was inspired by the Civil War prison dead lines, or made up independently.