Yay Rex. Sounds like they treat him like a 'rex' (ie king) how wonderful for him!
Yep I had a dog that sounded a bit like what poor mustard is going through. I was beyond upset. Like you I had placed a delightful dog and never really heard much. (though they did contact the rescue with a few issues, I suggested they go to Ado for training. They went but never followed her advice. If they had he would have been fine. Nope they decided to watch the dog whisperer...
I really hope Mustard comes back in much better shape than Joey did. They ruined him, he still isnt' normal and was adopted by people in the rescue because he is now unpredictable and has a serious bite history. I wish I could say Joey had a great outcome... But I don't think Mustard has been gone as long.