Further training of semi-skilled and skilled workers

Could you please answer my question about such a level as further trainig of semi-skilled and skilled workers. Is it vocational education? If it is, so what kind of education it is? (Upper-secodary education, post-secondary education or higher education?). I'm so confused, because it's written that the level  "Further training of semi-skilled and skilled workers" is in VET system and has ISCED 4B. ISCED 4 people can attain in post-secondary, non-tertiary education. But it's also written that there is no vocational education in post-secondary non-tertiary education. Thus, why this level "Further training of semi-skilled and skilled workers" is in VET system?