Introduced in 1910. Discontinued in 1917. I have never
seen this back design, apart from the image in Mrs. Robinson's booklet and the occasional sample card
in a salesman's sample folder or book. Very, very rare. The color in the red example above is generic.
The image for the blue card, above, is from a salesman's
sample card that sold on eBay for $225 on February 22, 2017, pictured below. This may be the closest
any of us get to a Margin Snowflake card.