Scenario Challenges

Scenarios are made up of groups of 3 people (at least that's the case so far in the Theramore event pre-Mists of Pandaria). In order to get guild credit for doing the scenario the entire group of 3 has to be guild members. We did a few runs with just 2 guild members and a pug. No guild credit. But we had a 3rd guild member want to come along and then we started getting credit with a full guild group.

Is it still possible to get this achievement in WoD? I know you can queue for scenarios in Pandaria, but I don't see any actual scenario challenges in the guild interface.

Surprisingly it does not take 3/3 to get guild challenge for a scenario. 2/2 or 1/1 works too. Must be all members in the scenario are of the same guild. I know this due to starting a scenario and the other 2 (random) members left before it even started. I decided to solo it and upon completion my guild got a guild challenge.