When my current guild was on a summerbreak, I had to find some way or another to get my shards for Shadowmourne.
So, I was in a weekly PuG who cleared 11/12 and last week we did 12/12. Also, just to add. Heroic bosses were: Marrowgar, Gunship, Saurfang, Rotface, Blood Princes and Blood Queen-Lana'thel. That's what I call a kick-ass PuG, we had tons of fun.