I highly doubt that everyone just missed China building another Xia...it's not easy to hide the money and resources going into a nuclear sub.
If there is a place in the world, that such circumstances can happen it is in China. Remember no one managed to post a picture of a second Chinese boomer until recently, and even then, half of the people would denounce it as some PS. [The GE picture of the boomer matches this picture, which confirms it as not being PS].
Even if people managed to take pictures of the sub, there is fear of recrimination of the pics were posted in some forum. Webmasters may take it out, and posters may feel they may get jailed. Once after the PLAN made the Type 093 sub formal, we have like two or three pictures suddenly emerging out of the woodwork. This case shows that Chinese internet forum goers are still intimidated about government censorship, even though, some people had no problems posting the Type 054A frigate in construction pics.
Another problem lately is that the PLAN have removed all the visible pennant numbers in their subs, into pennants that are so small you have to walk up the sub to see them. Thus if I see pictures of black subs for example, its impossible to tell if the pictures are only about one sub, two, or three or more. You only know and confirm that at least this class of sub is in the water, and at least one of them, but identification for more is difficult.
I don't think China built another Xia like the Xia 406. The report that there is a second Xia after 406 is just that, a rumor, and so is its alleged demise. 406 was a test bed. We know the value of earlier reports. They also claimed similarity to the Victor III and alleged Russian help. Now when pictures are revealed, the 093 looks a lot more like a 688 that it can be mistaken as such, than a Victor III. That sizes you the value of such reports, especially from Jane's.
This does not mean that much later, that they will build another, an improved Xia intended as a testbed for JL-2 firing. By then their technology would have been more mature.