Where the noun is followed by a postnominal adjective phrase or by a di-PP, the plural enclitic nan either follows the head noun directly, or follows the postnominal material. The plural marker cannot follow other PPs or relative clauses. Muller (1989, in Homenahe) shows that Noun + Adjective combinations which have compound-like interpretations take the plural marker after the Adjective. Muller (1989, Inleiding) shows that plural marking in the case of Noun + di-PP depends in part on the function of the di-PP: where the di-PP is a possessor, plural follows it. Where the Noun+ di-PP is a phrasal compound, nan either follows the head noun or the di-PP.
Reduplication is marginal as a device for creating plurals, and usually involves secondary connotations such as accumulation and scattered presence.
Source: Muller 1989: 542