As far as I know, it only applies to Nanning of Guangxi province. However, don't rule out other cities of said province doing so too. Local recruiting agents will likely be aware of the actual situatiom on the ground there, where they operate, as will those in other areas of China.. But as always here, things can change suddenly, and even without any prior warning, as is mentioned on the Chinese Foreign Affairs Office website. They state there that they are under no obligation to provide advance warning of changes in visa regulations to visa applicants. And it has been known for individual visa offices and PSB's to interpret said regulations in a different way, seemingly arbitrarily in some instances!

Please don't tell others. I have received privileged information that I'm only too willing to share with you!
The PSB of ****ing city of Guangxi province lets foreigners teach at public educational establishments until their L visas expire. Then they will replace them with Z visas, and simultaneously issue 180 day RP's, which can of course be extended in the city of issue, either with the same employer, or with another employer in said city, or both! This is really good news - no need to run to HK for a Z visa. Maybe other cities and towns of said province will do likewise. I do hope so, and that some other provincial PSB's will do so too.
I'm sure local recruiting agents will know the score re Guangxi. Those of you who are good at solving crossword puzzles and have been teaching in China for a year or two may be able to identify the city mentioned above.
It seems that at least one PSB is reverting to pre-Olympic practice re the issuance of Z visas on mainland. Fab news. The more the better!