I built me a comannder deck for Athreos, God of Passage. I did some searching for ways to get card draw (because I was running out of cards) and one of the card I looked at was Yawgmoth's Bargain.
I am always careful to check to make sure that the card I want to play is legal. So I loaded the "Sets and Legality" tab for Yawgmoth's Bargain. Since it is listed as legal for comannder, I bought the card and have been happily playing it in my commander games.
Frustrated that I had missed this I went back to the "Sets and Legality" page on Gatherer to double check. As you can guess, the card is listed as "Legal" for Commander.
So, which one wins? A ban list on a web page, or the Gatherer card database?
NOTE: I am happy to get opinions on this. But what I really want is a rule to says which one is the authoritative source of legality. (Without a rule, we are all just giving opinions right?)