Shown above is a detail image from the back of an interesting variety of this card reported to me by Jerry Anderson. It was originally printed incorrectly, bearing "No 56", which should be for Maryland. It appears that this error was discovered before the cards were distributed, and that a sufficient number of these were wrong to make it worthwhile for the lithographer to create an overprint to correct the error. Two solid bars were printed over the original "No 56", and the correct number for Oregon, "55", was printed to the right of it.
This type of overprint correction has also been found on the Maine (#52), Pennsylvania (#54), Maryland (#56), West Virginia (#57), Louisiana (#58) and Florida (#59) cards in this series. Please see the Errors & Curiosities - State Maps page to view examples. I'd be very interested in hearing from other collectors who've run across similar misprints on this and any other Arbuckle cards.