I'm afraid I don't follow either. I meant that in Japanese spelling a word is just saying it, not anything about how words are romanized, etc.
That is, you say the word たに by saying た and then に, and you say the word たんい by saying たん and then い. Equivalently if you were to "spell" the word きゅう you'd say きゅ and then う -- you wouldn't say き・ゆ・う because that would be a different word.
(Incidentally na and n'a are not pronounced the same, as the previous example hopefully illustrates.)
That is, you say the word たに by saying た and then に, and you say the word たんい by saying たん and then い. Equivalently if you were to "spell" the word きゅう you'd say きゅ and then う -- you wouldn't say き・ゆ・う because that would be a different word.
(Incidentally na and n'a are not pronounced the same, as the previous example hopefully illustrates.)