  Many natural and artificial systems whose range of interaction is long enough
are known to exhibit (quasi)stationary states that defy the standard,
Boltzmann-Gibbs statistical mechanical prescriptions. For handling such
anomalous systems (or at least some classes of them), {\it nonextensive}
statistical mechanics has been proposed based on the entropy $S_{q}\equiv k
(1-\sum_{i=1}^Wp_i^{q})/(q-1)$, with $S_1=-k\Sigma_{i=1}^{W} p_i \ln p_i$
(Boltzmann-Gibbs entropy). Special collective correlations can be
mathematically constructed such that the strictly {\it additive} entropy is now
$S_q$ for an adequate value of $q \ne 1$, whereas Boltzmann-Gibbs entropy is
{\it nonadditive}. Since important classes of systems exist for which the
strict additivity of Boltzmann-Gibbs entropy is replaced by asymptotic
additivity (i.e., extensivity), a variety of classes are expected to exist for
which the strict additivity of $S_q (q\ne 1)$ is similarly replaced by
asymptotic additivity (i.e., extensivity). All probabilistically well defined
systems whose adequate entropy is $S_{1}$ are called {\it extensive} (or {\it
normal}). They correspond to a number $W^{\it eff}$ of {\it effectively}
occupied states which grows {\it exponentially} with the number $N$ of elements
(or subsystems). Those whose adequate entropy is $S_q (q \ne 1)$ are currently
called {\it nonextensive} (or {\it anomalous}). They correspond to $W^{\it
eff}$ growing like a {\it power} of $N$. To illustrate this scenario, recently
addressed, we provide in this paper details about systems composed by $N=2,3$
two-state subsystems.
