I only read a small part of this topic so far because it is very long. For Berbice Dutch it is also hard to decide if [ŋ] is a phoneme or not. The phoneme could be [ŋ] or [ŋg]. If a word with [ŋg] plus final vowel is shortened it looses the /g/ and the vowel. A word with [ŋk] and a final vowel would only use the vowel. It works the same way with /nd/ and /mb/ or /nt/ and /mp/. I don't know if every combination is attested. Somebody wrote a complicated assay about that matter. [ŋ] does not occure indepentently.