Are 万葉仮名 (man'yōgana) chosen consistently?


[This answer](https://japanese.stackexchange.com/questions/15230/is-there-a-
kanji-for-%E3%81%97%E3%81%8B) got me wondering how relevant the presentation
in 万葉仮名 is to finding a 漢字 for a given word.

As far as I understand, 万葉仮名 are used largely for phonetic value. Knowing that
some word was written with some combination of 万葉仮名 would only carry any
significance if words were written consistently with the same characters. Do
texts in 万葉仮名 indeed choose 万葉仮名 consistently or is a lot of the choice a
stylistic choice on part of the author?




According to [Wikipedia](http://en.wikipedia.org/wiki/Manyougana), it would
appear that there were in fact a wide range of characters used for any given
sound prior to the de-facto standardization that was the creation of the Kana
syllabaries (keeping in mind, of course, that at their roots the kana
characters are either cursive forms of characters [ひらがな] or isolated elements
of characters [カタカナ]).

That said, it's interesting to note that from a historical perspective the
system pretty clearly differentiates between two versions of the vowels `i`,
`e`, and `o` for most columns. So in that regard there was some consistency,
but other than that it really was a matter of stylistic preference.

