In this post, "definite" refers, with regards to noun-phrases, to the quality of being a referent whose identity is known to the listener of an utterance. "Specific" refers to the quality of being a referent known to the speaker.
Ćwarmin and Bryatesle seem to have evolved definiteness marking in their case systems during times of contact. Ćwarmin's indefinite/specific/definite-distinction seems to go back fairly early, though, but we find dialects in contact with Bryatesle sometimes missing the specific/definite or the specific/indefinite distinction. The stage at which definiteness started becoming a thing in the Ćwarmin branch and Bryatesle-Dairwueh must be around the time of proto-BD, but later than Astami began diverging from the rest of the Ćwarmin languages.
Different languages in these groups have, however, dealt somewhat differently with definiteness marking on proper nouns. Proper nouns are most often definite by nature. In Ətimin, proper nouns are not marked for definiteness at all, with a few toponyms as exceptions. Rasm'in' and Ćwarmin, however, tend to use definite case marking for proper nouns in cases other than the core cases nominative, accusative, genitive and dative. The genitive and dative are flip-flopping in both, though. In these languages too, some toponyms have names where even the core cases are definite. However, exceptionally, Rasm'in' has a toponym that is always specific rather than definite, viz., mworanyus ädʒiniis', '(these/some) property markers of the belly', a historical border marker between the Kəlkəj and Moduwt tribes. The 'belly' refers to this being the most 'central' of the border markers between the tribes.
In Ćwarmin, personal names sometimes may appear in the specific. This, oddly enough, tends to indicate that the person referred to is a very recent acquaintance of the speaker, and that the speaker therefore is not sure whether the listener knows the referent.
With non-nominatives in Bryatesle, the definite case is almost always used with definite proper nouns except toponyms (and even there, many toponyms are definite - e.g. Zgakintën, 'the hilltop', a very definite hilltop near the capital. Omission of the definite marker, if no other secondary case takes its place, indicates specificity in non-nominatives. For nominatives, the partitive secondary case serves to indicate specificness.
One final language to consider is Dairwueh. It too has a very limited definiteness marking in the differential object marking of transitive subjects - genitive for definite, transitive subjects. It turns out a similar pattern holds there - nominative indicates specific, genitive indicates definite.