Can quality defects of released APIs that are identified by another entity belonging to the same company be handled outside of the API manufacturer’s complaint procedure?

Yes. After the release of an API for further use, any identified quality defect should be investigated and addressed according to the API manufacturer’s complaint system or equivalent (i.e., non-conformance, deviations, etc.) [ICH Q7, Sections 15.10 to 15.12]. Where equivalent systems are used, such defects should be categorised in a manner that provides clear visibility that the defect was discovered after being released by the API site.