Industry 4.0 and the rise of collaborative value chains necessitate seamless data integration across organizational and technological boundaries. Yet the fragmented standardization environment prevents interoperability across systems and within frameworks like the Digital Twin (DT). While the Asset Administration Shell (AAS) and Open Platform Communications (OPC) Unified Architecture (UA) are established as core standards for digital asset representation and communication, their independent origins and differing metamodels create semantic gaps that hinder unified machine-level understanding. This systematic mapping study examines how Knowledge Graphs (KG) can bridge semantic gaps to create unified semantic models. Current research demonstrates progress in pairwise integrations, such as transforming OPC UA models into RDF graphs or synchronizing AAS repositories with graph databases. However, these efforts often remain isolated solutions that address specific integration challenges. Consequently, large-scale industrial deployment remains limited. This paper consolidates current knowledge on integrating AAS, OPC UA and KGs, contextualizing these efforts and highlights research gaps toward achieving interoperable manufacturing ecosystems.