You just don't give up, even when you've been proven wrong!
Your own sources says that the Statuta Valachorum (the agreement with the Vlachs) was "never put into practice." History says that an agreement between Maria Theresa with the Serbs WAS put into practice.
2+2=4 Dio. Perhaps it's math, along with history, that you are having a problem understanding.
You OTOH, are suggesting that they didn't arrive until Maria Theresa. Can you please show us the arrangement and straighten this matter out?