What makes a requirement binding here
None over any manufacturer. WHO is a United Nations specialised agency and its pharmaceutical quality standards are recommendations to Member States, published as annexes to the Technical Report Series of the Expert Committee on Specifications for Pharmaceutical Preparations — WHO GMP for pharmaceutical products appears as TRS 986 Annex 2, and WHO GMP for sterile pharmaceutical products as TRS 1044 Annex 2. A TRS annex is a recommendation until a national authority makes it national law.
Two distinct ways, and conflating them is the common error. First, by national adoption: many authorities, particularly where no domestic GMP code was written from scratch, adopt WHO TRS annexes into national regulation, at which point the requirement is national law carrying a WHO text. Second, by procurement: WHO Prequalification assesses products and manufacturing sites so that UN agencies and national procurers can buy against a single assessment. Prequalification is a purchasing qualification, not a marketing authorisation — a prequalified product still needs national registration wherever it is used.