The dental nasal [n] became the velar nasal [ŋ] before velar consonants (SD/420). This [n]-assimilation was in fact the main way in which the velar nasal arose (SD/432). Similarly, the dental nasal [n] became labial [m] before labial consonants, with the sole exception of the combination [nw] (SD/420). The survival of [nw] may have been due to Elvish influence, since this combination was favored in Elvish languages. It is possible a similar [n]-assimilation rule applied to palatal consonants (SD/432-3), but these consonants later became dental, returning any altered [n] back to its original value.

Note that labial [m] did not assimilate to following consonants (SD/421). Such assimilation was not possible for velar [ŋ] because it could only appear before other velars, never consonants of other series (SD/432). Therefore, this nasal assimilation rule only applied to [n].

As this rule preceded other changes (further nasal assimilations), it likely happened early.