@FilipinoChatAdmin
Yes, the abbreviations can be tricky.
In school we were only taught "nito, niyan, niyon", which are the possessive forms of "ito, iyan, iyon". However, when we are engaged in conversation, except for "nito", the "i" in the other words tend to "disappear". That's because in making the sound of "y", the sound of "i" seems to already blend with it. So eventually, in informal writing, we started writing, "niyan" as "n'yan", "niyon" as "n'yon", "iyan" as "'yan" and "iyon" as "'yon". Though not too often, "ito" also gets written as " 'to".
Then comes the way we actually pronounce them. "Niyon" sounds a bit like "niyun", and "iyon", a bit like "iyun". Thus the " 'yun" and "n'yun" appeared, which then get written and pronounced as just "yun" and "nun".
There is also the "noon" that means "then (a time in the past)", that gets written and pronounced at times as just "nun". This comes out as a duplication of the "nun" of "niyon". For us native speakers, it's not a problem because we can easily figure out which is which based on context. However, for beginners, I can understand how they can cause confusion.
In formal writing, it won't be a problem because the original forms are normally used or, at least, the apostrophes would be indicated.
