The transformation from analogue to digital data is the core principle of the digital turn in the sciences and humanities. Within numismatics, this is visible in projects to digitise coin collections and publish them in online catalogues (e. g. IKMK and KENOM), or in coin find databases (e. g. AFE-RGK). The project nomisma.org was founded to promote and support the application of LOD within numismatics, and is now firmly established internationally as the primary resource for the domain. Drawing on the vocabulary and ontology of nomisma.org, a range of web-based resources, such as OCRE for the Roman Imperial coinage, now translate individual coins from instances in collection or find databases to exemplars of standard typologies or classifications,. However, in contrast to the coinages of much of the Graeco-Roman world, for which well established classifications exist, the lack of a single, universal classification for Celtic coinages presents a range of challenges. Instead there are a number of classifications for individual coinages and regions, many of which cannot be mutually reconciled. To address this, the BMBF cooperative project ClaReNet is developing a nomisma-conform virtual union catalogue, Online Celtic Coinage (OCC) to provide both a human-user friendly resource and machine-readable, re-usable data for the semantic web (LOUD and FAIR). This presents not only a unique opportunity to attain interconnectivity between the disparate classifications of analogue publications, but also to incorporate contextual, in particular the archaeological information (distribution, findspot) that is essential for establishing the chronology of Celtic coinages and understanding their use. Taking OCC as an example, this paper aims to explain how we would define LOD usability for Celtic coins and how data from different contexts of collection can be brought together in a virtual union catalogue.