I still think that there's little reason to believe there was ever any card trading code to base Mt. Gox on in the first place.

I've only looked into this a little bit, but the more information I find the more it seems like the relationship between Mt. Gox and Magic: The Gathering Online Exchange has been greatly exaggerated, perhaps to a downright comical extent. See: https://news.ycombinator.com/item?id=7215940