Intelligence-based sketch. The new construction halls (A) are at the center of the site. Thailand's new submarine is likely to have been built in the hall nearest the river (B). The submarines are rolled out of the sheds on rails (C) and launched sideways into the river (D). They are moored alongside to be fitted out (E). Expansive new halls are still being built in several areas of the site (F). Civilian ship building largely takes place in the open (G).
They might have added a few more after 2017. PLAN went stealth mode plus tight control on the media with regards to submarines since then. Its not like years ago when there was plenty of pictures of submarines.
From what I think is that the entire Yuan class fleet went into a refit except for the newest ones which didn't need to. The older ones, the ones with the squarish sails, were refitted with new sails that have the curved and webbed corners. From this time on, the number of pictures of the square sailed Yuans dramatically dropped, and most of the pictures you see now are the ones with the curved sails. Upgrades might also include other things within the submarine.