No text, but a visual code

[Emma May Smith]

...
  Emma did a bright analysis about (o),(a) and (y or 9) as the same class of character. They are complementary and occur in the same position in the word. I think all of them stand for the stars in different positions or moments.

This is not quite correct and I don't think you are interpreting Emma's work correctly.

The "o" and "9" behave in certain ways that are similar in certain positions, but you will NOT find the "o" at the ends of words in the same way as the "9" and you certainly will not find the "a" behaving like "o" or "9", it has its own unique patterns. Nor will you find the "o" following "8" at the ends of words in the same way as "9".

The glyphs a and y are complementary in distribution: they typically don't appear in the same environment. This suggests that they could be variants or closely linked glyphs. However, if you take these two glyphs to be halves of a single a / y glyph, then that a / y glyph is in contrastive distribution to o. This suggests that they have different meanings but belong to the same functional class of glyph.

I therefore consider it odd if any discussion of y doesn't also discuss a and o, in different ways.