Regardless 1,2 or I, II, the type is 09. Using Arabic numerals after 09 would be confused to type 091 and 092 which was never PLAN's designation. Besides, we have never seen official publication using either numerals. 091 or 09II are all outsiders usage. Therefor, for our convenience only.The 091 and 092 retain Arabic numerals. It's only from 09III on that the designation system switched to roman numerals. Other than that, I quite like the graphic.
As of the switching, what is the story of it? when was it changed? Can you elaborate? I am just curious.
P.S. here is an article in Chinese (if you read) which is quoting a report from PLA daily
The reason of "type" 09 was because the nuclear sub program was the "number 9 (critical) program", so all nuclear subs are "type" 09.