Why not positional variation?

[ReneZ]

Because we all know that daiin is more of a language A word

The two most frequent words in the last quire of the MS, the long stars- or recipes section, are aiin and daiin respectively. The third on the list is qokaiin, though this may depend on the transliteration. This part is written in the B language.

Mauro pointed out that it depends strongly on what comes before -aiin, and arguing that it is a language issue may or may not be consistent with that. This would require showing that these words are language-dependent.