  e+e- experiments at charmonium production threshold are reviewed, it is found
that the contribution of the continuum process via virtual photon has been
neglected in almost all the experiments and most channels analyzed. It is
pointed out that the contribution of the continuum part may affect the final
results significantly in psi(2S) and psi(3770) decays, while the interference
between the continuum amplitude and the resonance amplitude may even affect the
J/psi decays as well as the psi(2S) and psi(3770). This leads to the revise of
the analysis of strong and electromagnetic amplitude in psi(2S) decays,
including psi(2S) ->VP which is the long lasting puzzle between J/psi and
psi(2S) decays. For psi(3770) physics, a large constructive interference for
light hadron modes and destructive interference for DDbar could be responsible
for the discrepancy between the larger cross section of inclusive hadrons by
direct measurement of e+e- -> psi(3770)-> hadrons than the DDbar cross section
measured using D single-tag and double-tag method.
