Every visa is man made and nothing comes from heaven. All things are possible unless you make foreign teachers miserable. There is no black listed Foreign Teachers anywhere in the world. But we know there are many blacklisted employers or schools especially in China. What you know about issuing visas at a PSB is your own regulations. I don't believe in everything you say but I know China's L visa from Macau has been changed from 30 days to 7 days.