BBB Etymology - Dead as a Door Nail

"Old Marley was as dead as a door-nail.

"Mind! I don't mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail. I might have been inclined, myself, to regard a coffin-nail as the deadest piece of ironmongery in the trade. But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country's done for. You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail."

Other than this reference in a classic Dickens' tale, from whence does "dead as a door nail" come? My favorite etymological story is this ... Nails were once hand tooled and costly. When an aging cabin or barn was torn down the valuable nails would be salvaged so he could reuse them in later construction. When building a door however, carpenters often drove the nail through then bent it over the other end so it couldn't work its way out during the repeated opening and closing of the door. When it came time to salvage the building, these door nails were considered useless, or "dead" because of the bend.