Paradoxically, Digital Editions as well as digital archives, tools, platforms and data repositories are not as interoperable in practice as one would theoretically expect from standardised sources. To be able to cross- or re-use data or tools between projects, in practice, serious refactoring and rededication is necessary – e.g. existing web platforms cannot readily be re-used by another project, notwithstanding the fact that the data repositories are fully validating, validating TEI-P5 sources. How is this possible?