This paper tests two hypotheses: (1) the normalized Pairwise Variability Index (nPVI) values computed on the basis of recorded performances may be higher than the nPVI values computed for the same works as musical scores, and (2) the musical nPVI values for different composers may vary substantially within one culture even within a short time-span. In Study 1, samples from the vocal works of four Estonian composers, Artur Kapp (1878-1952), Mart Saar (1882-1963), Eduard Oja (1905-1950) and Eduard Tubin (1905-1982) were used for calculation of nPVI on the basis of both scores and performances. nPVI values for performed music were higher than those for scores but the differences were rarely statistically significant. In Study 2, larger corpora of scores by three Estonian composers: Saar, Tubin, and Veljo Tormis (born 1930) were analyzed. Songs by Tormis had significantly lower nPVI values than those by Saar and Tubin. Our results imply that calculation of nPVI values in music may rely either on a score or on a performance, the results being not significantly different from each other. The results also show that there may be significant differences in rhythmic contrast between the works of composers from one culture created only a few decades apart, and that nPVI values may not only increase but also decrease for compositions created later in time.