Loving the Toryu pics you found there
I believe the order of kanji used in 'model' developmental denotation is...
Ko, Otsu, Hei, Tei, Bo, Ki etc (in the phonetic order in Kanji, aka a kanji-betical equivalent of A, B, C, D, E, F etc).
Note, the Ki in Kanji, is not to be confused with the 'Ki' abbreviation for Kitai or 'Type' (Year of Service Acceptance Type) designation, where the 2 numbers correspond to the (Ancient) Japanese calendar where 1940 = 2600 IIRC.
Also with the Japanese naming systems depending upon the war situation, sometimes latter models had less weaponry, ammo, kit or a mix of bits and bobs missing and swopped back from earlier models with newer developments too, so following the models/marks kit progression won't always highlight an actual model type to 100% certainty.
I'm Shin-senpai or other members can provide the correct terms, if searching online isn't quick enough.