In all versions of Quenya from the 1910s through the 1960s, any initial nasal + stop clusters (excluding only those that became syllabic) reduced to simple nasals. Tolkien described this change all the way back in the Qenya Phonology written in the 1910s (PE12/15-16) and there are numerous examples of it in the Qenya Lexicon, The Etymologies and throughout Tolkien’s writing. A fairly complete description of this change appears in the Outline of Phonology (OP2) from the 1950s with a representative set of examples:

These groups in Quenya normally became simplified to nasals initially. (In Telerin they became b, d, g.) Thus:

• mb- > m, as in *mbar- > Q már “habitation”.
• nd- > n, as in *ndōrē > Q nóre “country”.
• ñg- > ñ, as in *ñgolodo > Q ñoldo “Noldo, Gnome”.
• ñgy > ny, as in *ñgyar- > Q nyare “recites”.
• ñgw > ñw, as in *ñgwar- > Q ñware “frets, wears away”.

The full medial development > mb, nd, ñg, ndy, ñgw still appeared in AQ in the second element of compounds after a preceding vowel, and after vocalic proclitics such as especially the article i (AQ iñgoldo “the Gnome”). The retention of the medial forms was still frequent in PQ, surviving in many cases, especially in old names, in TQ. But the initial forms tended to spread, even in compounds, and in the case of proclitics, such as the prepositions, the article, or grammatical augments in verbs, were generally substituted in PQ and TQ (OP2: PE19/76).

A very similar description appears in Outline of Phonetic Development (OP1) from the 1940s (PE19/35-36). OP1 indicates that the reduction to simple nasals occurred in AQ, and OP2 effectively says the same thing, with the addendum that the full combinations survived longer in compounds. These phonetic developments were mentioned in many other places in Tolkien’s writing (e.g. PE17/123; PE18/103; PE22/112).

In OP1, Tolkien mentioned that same change occurred for initial nasals + voiceless stops (PE19/35), an idea that reappeared in the second version of Tengwesta Qenderinwa (TQ2: PE18/92) and the first drafts of OP2 (PE19/76 note #40). But Tolkien seems to have decided that nasals + voiceless stops were no longer a valid initial combination in Primitive Elvish (PE19/77 note #45, PE19/78 note #48 and #49).