My high school Balarila differentiated the words ng from nang as used in the following examples:
Perlas ng silanganan (Pearl of the orient)
Nang si Jesus ay isinilang (When Jesus was born)
However, I believe ng started as a contraction or abbreviation of nang. Check The Project Gutenberg Ebook of Ibong Adarna, by Anonymous. Out of more than 19,000 words in more than 5,400 lines of this work, “nang” appears 618 times, 3 times in the subtitle:
CORRIDO AT BUHAY NA PINAGDAANAN NANG TATLONG PRINCIPENG MAGCACAPATID NA ANAC NANG HARING FERNANDO AT NANG REINA VALERIANA SA CAHARIANG BERBANIA
On the other hand, “ng” appears only once, in the following stanza:
Cun aayao magpa-silla
ang cabayo’i, mag-aarma,
palo’t, dagoc na lahat na
ng gauin mo sa caniya.
Obviously, ng and nang may be used interchangeably. Whether the user wants to use either ng or nang to mean “of” or “when” should be determined by the context in which either word is used. As in other languages, there are words in Filipino that could mean different things under different contexts, e.g., bata for gown, or bata for child. So why the need to go out on a limb to differentiate ng from nang when, as in Ibong Adarna, they are one and the same?
[Coincidentally, “manga” appears 32 times in Ibong Adarna, while “mga” was not used at all. The conclusion is that “mga”, as used in current Tagalog/Filipino discourse, is a contraction or abbreviation of “manga”.]
I don't think, however, that the "NG" in the Filipino alphabet refers to the contracted or abbreviated "NANG". It is the digraph ng. A digraph, by the way, is a pair of letters used to write one sound or a combination of sounds that does not correspond to the letters combined, as in the following example: Ngunit ang tugon niya'y dalangin na walang hanggan (But his answer was a prayer without end).
The digraph "ng", however, is NOT unique to Tagalog or Filipino. It also occurs in English as in the following example: The singer’s raspy voice impinging on one’s bingo concentration.
Yet the digraph ng is not considered a unique phoneme in the English alphabet, or in some other Roman languages that use it simply because they don't have words that start with the digraph, one of three tests that a digraph must pass to be considered as a unique phoneme (the other being that the digraph may occur in the middle of the word or at the end). Some linguistic technicality--which is probably why the Komisyon sa Wikang Filipino insists that "language planning... should be a collaborative endeavor of scholars, linguists and practitioners in the study and use of the language." The ordinary language user--you and I--well, we're chopped liver! But then, that's another story.
While it may be difficult to find a "native" English word that starts with ng, the explosion of the Vietnam War into the global consciousness introduced us to non-native words that did so. Some of the words thrown about by the media during that war were proper Vietnamese names, like the Ngo's and the Nguyen's. Then 1976 saw the largescale migration of the Vietnamese--including the Ngo's and the Nguyen's--to the United States. Well, even as proper names starting with Ng may get entrenched in the public consciousness, they may not find their way into the lexicon of the English language to warrant the revision of the English alphabet to include the digraph ng.
I learned from a reliable language authority that the inclusion of ng in the Filipino alphabet is an effort to differentiate ours from others. Well, the Vietnamese have other ideas because they, too, have ng as one of 8 digraphs in their 37-letter alphabet where "A" with varying inflection marks is counted as 3 unique letters!
If we eliminate NG as a separate letter, er digraph, the 2001 revision of the Filipino alphabet is, for all intents and purposes, an adoption of the current 27-letter Spanish alphabet: A, B, C, D, E, F, G, H, I, J, K, L, M, N, Ñ, O, P, Q, R, S, T, U, V, W, X, Y, Z. In a nation where more than half the population have Spanish names, it certainly is difficult to understand the misguided bent of some of our intellectuals to try to distance you and me and themselves from the Spanish alphabet at some point and then grudgingly re-adopt it anyway.
So the Spanish alphabet is back. Plain and simple. And richer for the Filipino alphabet. In the exact words of the Komisyon sa Wikang Filipino: “The promulgation of this Department Order [2001 Revisyon] was regarded as a significant step in promoting more dynamic development of the language. The goal is lexical enrichment of Filipino by liberalizing word borrowings and translations largely from English and Spanish using eight additional letters of the alphabet, namely letters C, F, J, Ñ, Q, V, X, Z.” In a pragmatic sense, the revised Filipino alphabet is basically what we had before, before the likes of Lope K. Santos (who changed his middle name from Canseco to Kanseco) thought it was the “nationalist” thing to do to rid the letters C, F, J, Ñ, Q, V, X, Z from the Spanish alphabet and proclaim the emaciated 20-letter alphabet (with NG) as the Tagalog ABAKADA, then the official alphabet for the then Wikang Pambansa, which became Wikang Pilipino, which morphed into Wikang Filipino.
The sequence of events from the time Tagalog was declared as the basis for the evolving "national language" just reinforces Alexander Neville’s theory in Language, Class and Power In Post-Apartheid South Africa that a [national] language does not develop “naturally” as it were, but is something planned by those in power either through executive order, decree or legislation. Even as there obviously were some missteps in our language planning and policies. At any rate, I strongly recommend that “ng” be purged from the current Filipino alphabet as revised in 2001. We are not losing anything that’s worth a hoot, so let's just cut the mustard. Because it has a human-appendix-and-tonsil excuse for being. Purging "ng" certainly won't trigger cataclysmic fissures in the lexical landscape. It won’t diminish informal or formal discourse. From a learner’s standpoint, it’s one less letter (or whatever) to remember. Let the "scholars, linguists and practitioners in the study and use of the language" deal with their momentary grief on the loss of ng--and then let's all move on to meatier stuff. Such as refocusing our efforts in the development and enrichment of Filipino in the face of a runaway train called code-switching.
NG as a unique alphabet digraph, NO; as an ordinary digraph or as a contraction or abbreviation for nang, yes, ABSOLUTELY!