Today, annotated MIR corpora are provided by various re- search labs or companies, each one using its own annota- tion methodology, concept definitions, and formats. This is not an issue as such. However, the lack of descriptions of the methodology used--how the corpus was actually an- notated, and by whom--and of the annotated concepts, i.e. what is actually described, is a problem with respect to the sustainability, usability, and sharing of the corpora. Ex- perience shows that it is essential to define precisely how annotations are supplied and described. We propose here a survey and consolidation report on the nature of the an- notated corpora used and shared in MIR, with proposals for the axis against which corpora can be described so to enable effective comparison and the inherent influence this has on tasks performed using them.