  Within the realm of QCD sum rules, one of the most important areas of
application of this nonperturbative approach is the prediction of the decay
constants of heavy mesons. However, in spite of the fact that, indisputably,
the adopted techniques are, of course, very similar, we encounter rather
dissimilar challenges, or obstacles, when extracting from two-point correlators
of appropriate heavy-light currents interpolating the mesons, the
characteristics of charmed mesons with different spin. In view of this, it
seems worthwhile to us to revisit this issue for the case of charmed
pseudoscalar mesons $D_{(s)}$ and vector mesons $D^*_{(s)}.$
