Identifying versions of the same song by means of automatically extracted audio features is a complex task for a music information retrieval system, even though it may seem very simple for a human listener. The design of a system to perform this task gives the opportunity to analyze which features are relevant for music similarity. This paper focuses on the analysis of tonal similarity and its application to the identification of different versions of the same piece. This work formulates the situations where a song is versioned and several musical aspects are transformed with respect to the canonical version. A quantitative evaluation is made using tonal descriptors, including chroma representations and tonality. A simple similarity measure, based on Dynamic Time Warping over transposed chroma features, yields around 55% accuracy, which exceeds by far the expected random baseline rate.