Nagano, Yasuhiko. Cogtse Gyarong. 2003. hh:s:Nagano:Cogtse
Prenasalized stops/affricates and nasalized vowels are given as ɴP and Vɴ sequences in the source. It isn't clear which prenasalized stops/affricates exist; since the source says /ɴ/ "occurs before the stops and affricates", we assume it can occur before _all_ stops and affricates.