You made some good remarks though your elaboration is greatly hampered by your poor command of English. Your cited examples to sustain that metathesis of liquids has lasted even after 12th century A.D are very tenuous, so to speak. Accordingly, this is not an easy topic to nail down with some superfluous examples lacking from any skilful investigation. Indeed a more exhaustive and professional study is required, all the more so when metathesis of liquids – though not in great proportion – is attested even in Albanian. Truth be told, I am more inclined to believe that proto-Albanian (i. e the transitional stage from its Illyrian predecessor) was affected by such linguistic phenomenon at this time. So can anybody clear up for me to what extent took place this phenomenon in Albanian? If my memory serves well, in Albanian metathesis of liquids occurred in some words where the vocal is in the unstressed position (which is not the case with Slavic). The metathesis of liquids is best exemplified by the following examples mainly Latin borrowings: krasun > kërcu; fricare>fërgoj, etc. Whereas the name of medieval capital of Serbia, Raska features a pertinent phenomenon where Albanian has mediated from its pristine form ARSA (as it is attested in Procopius writings) through the regular evolution /s/>/sh/ as well as the Slavic metathesis a – r > r – a. It would not be amiss to surmise that proto-Albanian groups were quite dominant in these areas as to affect Slavic in some scale.

The region Labëria is usually etymologized from Greek Αλβανία (Albania) where:
i) The Bulgarians have operated the LM Albania > Labania and the Tosk Albanians have operated the rhotacism of intervocalic -n->-r- Labania > Labëria as in Avlona > Vlonë > Vlorë.

I wholly agree with your analysis. To my humble opinion, the same phenomenon has taken place also in Labunishtë (an Albanian village in nearby of Struga), where a metathesis from a previous *alb to LAB is quite likely.

But the problem is that in order for the Greeks to call the place "Albania" in the first place, there must be Albanians living there and no historian admits that there were Albanians in what is modern south Albania before 1100 AD.

hmmm…you just go off at half-cock without taking into account additional proofs. The claim that Albanians trickled in great numbers in Epirus is untenable at best as it falls short of convincing for a myriad of reasons. Thus it is a skewed logic to assume that Albanians came out of the blue in Epirus by changing drastically its previous ethnic make-up. A more clear-eyed investigation would surely reveal that some proto-Albanian pockets were to be found in Byzantine Epirus much earlier than it is admitted. Your source clearly stated that:

This Arbanon, the Raban of the Life of Stefan Nemanja, was a land without direct access to the sea, even though the coasts of Epiros, despite their control by Serbs and Greeks, remained primarily inhabited by Albanians, as did the mountain areas which rose above the eastern shore of Lake Shkodër (Scutari), in Latin Polatum, in Slavonic Pilot.

The so called Jirecek line where allegedly all areas south of Shkumbin River were Greek-speaking is a gross oversimplification. Several studies which dwell on that problem hammered home the same conclusion that Epirus populace has dwindled away since 168 B.C. The Byzantine Greek-speaking element out there jumped up especially after 1204 A.D when Constantinople was captured by Latins. It is not unlikely to assume that a large chunk of Epirotic population which found asylum in the mountains of Albania, with the drift of time was creeping in its previous homeland. A startling evidence is to be found in the place-name Σχόδρα in NW of Jannina as it has been noticed by Georgacas. 

So the south slavic LM has occured sometime after 1100 AD.

Not so, amigo! It is patently obvious that a certain ARBANIA existed out there much earlier than 12 century. What matters the most is that the region in vicinity of Vlora was called by its inhabitants as ARBERIA and it would not be a misnomer to state that the old Bulgarian document meant exactly the inhabitants of this region of Epirus which was left out of the Bulgarian orthodoxy.

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