  We discuss the idea that the Tsallis-type (q-additive) entropic chain rule
allows for a wider class of entropic functionals than previously thought. In
particular, we point out that the ensuing entropy solutions (e.g., Tsallis
entropy) can be determined uniquely only when one fixes the prescription for
handling conditional entropies. Our point is substantiated with the Dar\'otzy's
mapping theorem and DeFinetti-Kolmogorov theorem for escort distributions and
illustrated with a number of examples. Connection with Landsberg's
classification of non-extensive thermodynamical systems is also briefly
discussed.
