Ok, time to bring this thread to its initial purpose...
Dibo, first of all, you should know that romanian theories about the southern vlachs are very moderate, unlike the transylvanian situation, because they are not inflicted by nationalism. Romania and Bulgaria have not a single territorial claim on each other, even the southern Dobudja, gained in 1913 and lost in 1940, was considered by the nationalistic movements as foreign land.
Ok, here are my thoughts....
Ist Problem. Southern Vlachs. Who were them, were did they live, accounts etc..
The first account on southern vlachs is a story concerning Kastamunitu Monastery in Athos, which mentions vlahorinhini in the VIII century. Their identity is pretty much proven because of a single word which is latin-based and seems to be part of their language. The accounts will continue with the killing of David, son of Sisman, in 976 by some vlachs and with Niculita, which becomes lord of the Thessalian vlachs in 980. In the next centuries, vlachs will be frequently mentioned by the byzantines.
Ok, they exist. Where did they live? From all the documents, it seems that vlachs dwelled a rather large territory (of course, they were sheep herders, so "dwell" is not the best expression, they did move a lot), meaning Thessalia, Thrace, Calcidic Peninsula, Epirus and Macedonia. Thessalia, for example, was referred to as "Great Vlachia".
In 1066 Kekaumenos labelled them as descendants of dacians and bessians, treacherous to the romans as their ancestors, who left from Danube to Macedonia and Epirus. So, vlachs knew their history and recorded their origins.