Identifying and monitoring Open Access (OA) publications might seem a trivial task while practical efforts prove otherwise. Contradictory information arise often depending on metadata employed. We strive to assign OA status to publications in Web of Science (WOS) and Scopus while complementing it with different sourcesof OA information to resolve contradicting cases. We linked publications from WOS and Scopus via DOIs and ISSNs to Unpaywall, Crossref, DOAJ and ROAD. Only about 70% of articles and reviews from WOS and Scopus could be matched via a DOI to Unpaywall. Matching with Crossref brought 53 distinct licences, which define in many cases the legally binding access status of publications. But only 53% of publications hold only a single licence on Crossref, while more than 42% have no licence information submitted to Crossref. Contrasting OA information from Crossref licences with Unpaywall we found contradictory cases overall amounting to more than 13%, which might be partially explained by (ex-)including green OA. A further manual check found about 17% of OA publications that are not accessible and about 15% non-OA publications that are accessible through publishers’ websites. These preliminary results suggest that identification of OA state of publications denotes a difficult and currently unfulfilled task.