No, they have actually not mentioned the diesel buses in connection with the check. Only gas. 200 buses per day will not be a massive amount as it regards the whole country.
If you have lived here in over 20 years, I have over 24 years, then you would know better, and not use the word allow. Where have they allowed anything? You have seen soo much, but you still not understand that the ones that wish to modify do that, without anybody allowing anything. What is wrong, is that they do not do regular checks, outside the yearly one, when I am sure the tanks are removed to make buses pass inspection or money given to pass or just not checked. Still, the government is not allowing this.