Diachronic notes
Anthologica Universe Atlas / Universes / Our World / Kuchean / Kuchean / Diachronic notes

However, masculine nouns denoting rational beings have secondarily created a distinct acc. sg. in PT *-nə > TB -ṃ, TA -(a)ṃ. This ending, which has also been extended to most acc. sg. adjective forms, goes back to n-stems formed with the PIE individualizing suffix *-on (cf. the development of the Germanic weak adjective inflection).

Masculine nouns denoting rational beings take -n. Does this extend to *all* acc. sg. adjectives, or just masc. rat.?
However, "all non-neuter accusatives end in -ṃ in TB".

in TB the instrumental is expressed by the perlative /-sa/. The TB “causal” is found with only a few abstract nouns, e.g. läkle-ñ ‘because of suffering, out of suffering’, and best treated as a fossilized case form.

There will be some lexicalized items with -ñ, but this won't be productive.