The only visible difference that I can see is the elimination of the windows in the sail and addition of the sail 'cusp', but that was also done in the 093A. The original 094 already had the towed sonar array.

I don't know if the 093B1, B2, etc. designations are official or not. Also, there are very few photos of the 093B 'mini turtleback' and the only ones I have seen are not clear enough to rule out photoshopping to make the 'mini turtleback' look bigger - I suspect the 093B and B1 are one and the same (look at the pattern of the limber holes) and the so called '093B2' is just a 'flight 2' version of the original 093B, with a thinner towed sonar that uses a smaller reel and therefore a smaller 'mini turtleback'. JZCS is probably right to lump all 093B together.

How many of each subclass were built? As far as I know, there were only two original 093 and a single 093A with no towed sonar, all others were some 093B variant. I don't know anything about 094 versus 094A, but in total PLAN has at least 10-12 SSNs including the latest 091 (which will probably all be decommissioned in the next five years).

Could earlier versions of 093 fire YJ-18, or did the capability only start with 093B?