Electroacoustic music and computer music come along with a vast variety of sources ranging from traditional score to complex digital performance set-ups. Approaches of documentation and archiving yet have not only to deal with the challenge of the rapid technological developments that cause the urge of updates in order to provide access to the content, the constant need of transfer also raises basic historical questions such as e.g. what to consider and thus save as historical testimonies of a musical works and its performances and how to include this instability of the sources within the embedded information. In my contribution, I will reflect on the mutual influence of technological challenges, the state of source material, approaches to documenting and archiving, and what this can mean for establishing new performances of these musical works. Hereby, I am especially interested in a structural reflection on the relationships between these processes and the resulting sources, as well as the question what this can mean for the (future and past) appearance of a musical work.