Well, at best we can ASSUME the conversion must've taken place during the previous year. Because it's unlikely for such images to stay hidden for years? And then use that info to conclude at least one regiment worth of new planes was produced, displacing these planes. So, if enough of such images/news comes during a year, covering several different units, then one MIGHT make a conclusion as to what's the current combined procurement rate for PLAAF, annually. Sadly, we're simply not going to get as many images per year, if 2017/2018 activity is repeated in 2019.
I would assume at least three and likely not more than 4 units get new combat jets each year in PLAAF. Meaning probably as many other units get their hand-me downs as they become 2nd rate planes. And then 3-4 more units get THEIR hand-me downs, which are by then 3rd rate planes. Or these J-7Gs, as we're seeing now. And J-7IIs simply get either scrapped or stored. Actually I don't think there's more than 200 J7II/H left in active units today...