Can Australian OET really accumulate 4 B's?

It depends on the specific situation. The requirement of vocational evaluation is still to pass four B's at one time, and the Immigration Bureau will add 10 to the language, which is so loose that four B's can be accumulated.

Considering that skilled immigrant applicants must pass the vocational assessment, they can only enjoy the preferential policy of accumulating four B's in OET unless they are exempted from the vocational assessment (studying in English-speaking countries for five years).