Duels of the Plainswalkers is missing from the editions list and I can't list a few cards properly because of it (I'll have to use closest matching alternate)

It uses the same M symbol that a couple of other editions use.

Example cards affected:
Wurm's Tooth http://magiccards.info/dpa/en/97.html
Demon's Horn http://magiccards.info/dpa/en/91.html

Card list on MagicCards.info
http://magiccards.info/dpa/en.html

The issue is that all of the version information is pulled from the official Gatherer site, which does not list these types of versions/promos. At this time I don't know of any plans to add these additional editions.