I have recently come across 2 cases of those plastic retzuos which were first discovered about two and a half years ago. This is the type that has the thick plastic (not paint veneer) heat pressed onto poor quality leather that easily tears once it is separated from the plastic.
One was from a pair of tefillin purchased in NY , the other, from Israel. Both sets were a few years old and could have easily come from those fraudulent batches being sold a few years ago.
My theory is that some of them began splitting right away or within a short amount of time, so people changed them. Some people may also have tested them when the fuss was being made once the fraud was discovered, and changed them then. But in all likelihood, many did not, and if the two parts are still bonded together (some may have been manufactured better than others) then people would be unaware that anything is wrong.
The common pask on those retzuos were that they were possul.
I'm wondering if anyone else is still seeing them and if sofrim in general keep an eye out for them when people bring tefillin in for checking. Now that it has been a few years, these will start coming in for routine checking, and if they are still out there and have not been replaced, it is incumbent upon the sofrim checking tefillin to keep an eye out for them. If they look suspicious, they should be tested immediately.