  A systematic modification of the entropy trajectory $S_m(T)$ is observed at
very low temperature in magnetically frustrated systems as a consequence of the
constraint $S_m\geq 0$ imposed by the third law of thermodynamics. The lack of
magnetic order allows to explore some unusual thermodynamic properties by
tracing the physical behavior of real systems. The most relevant findings are:
i) a common $C_m/T|_{T\to 0} \approx 7$\,J/molK$^2$ 'plateau' in at least five
Yb-based very-heavy-fermions VHF compounds; ii) quantitative and qualitative
differences between VHF and standard non-Fermi-liquids. iii)
Entropy-bottlenecks governing the change of $S_m(T)$ trajectories in a
continuous transition into alternative ground states that exhibits third order
characteristics. An empirical analysis of the possible $S_m(T\to 0)$
dependencies according to the $\partial ^2 S_m/\partial T^2$ derivative is also
preformed. Altogether, this work can be regarded as an empirical application of
the third law of thermodynamics.
