Meillet gives tha as an example of grammaticalisation in his 1912 paper L' évolution des formes grammaticales, in which he introduces the term grammaticalisation. Na is covered in Haspelmath (1989), which draws on the extensive Greek linguistic literature on the subject (see above.)
I intend to show in my thesis that these adjuncts are better classified as circumstances.
There are various reasons why poetry is to be dispreferred in diachronic syntactic work (see Blake (1992) for arguments.) Unfortunately, early Modern Greek prose is extremely rare. I wish to concentrate on narratives because I feel they will maximise the occurences of (o)pu where it is an optional complementiser--since complementiser (o)pu, I will argue, is associated with the givenness of the complement; one would expect given information to be more frequent in narratives than, for example, devotional texts.
Shtokavian is one of the three major dialects of Serbo-Croat; these dialects are named after the word for 'what' in each dialect--shto, cha, and kaj.
I am not aware of any similar phenomenon in Albanian or Macedonian; but data from the Albanian and Macedonian dialects spoken in Greece should be quite interesting.
The nature of the source texts (mostly fables, contributed by the rural elderly) is probably too homogeneous to isolate variables other than geographic in the texts.
'Demotic' properly refers to the Greek vernacular before it began interacting with puristic, and to the prescriptive norm, based on this vernacular, set down by the demoticists--including Triandafyllidis and Kriaras, and to a lesser extent Tzartzanos.
The dialect spoken in Athens--a small town before 1830--was rather archaic compared to CSMG, and died out relatively early. The origins of CSMG are therefore to be sought amongst the people who settled Athens after it became the capital of the new Greek state.
This new prescriptivism is still quite healthy--Kriaras, editor of the Dictionary of Mediaeval Greek Vernacular Writing, is one of its major exponents. In conjunction with the politicisation of diglossia, it seems to have occasioned some morphological change in CSMG in the past twenty years. Thus, puristic morphological elements previously acceptable in Standard Modern Greek (for example, the vocative paradigm kathighita 'Professor, Teacher' (cf. Demotic kathighiti)) are now being rejected.