  We investigate laser-induced nonsequential double ionization from aligned
diatomic molecules, using the strong-field approximation in its length and
velocity gauge formulations. Throughout, we consider that the first electron
dislodges the second by electron-impact ionization. Employing modified
saddle-point equations, we single out the contributions of different scattering
scenarios to the maxima and minima observed in the differential electron
momentum distributions. We show that the quantum interference between the
electron orbits starting and ending at a specific center $C_{j}$%, and those
starting at $C_{j}$ and ending at a different center $C_{\nu}$ leads to the
same maxima as minima as if all possible scenarios are taken. There exist,
however, quantitative differences as far as the gauge choice is concerned.
Indeed, while the velocity-gauge distributions obtained employing only the
above-mentioned processes are practically identical to the overall
distributions, their length-gauge counterparts exhibit an asymmetry in the
positive and negative momentum regions. This asymmetry is due to additional
potential-energy shifts which are only present in the length-gauge formulation,
and which, depending on the center, sink or increase the potential barrier
through which the first electron tunnels. In contrast, the interference between
topologically similar scenarios leads at most to patterns whose positions, in
momentum space, do not agree with the overall interference condition, neither
in the length nor in the velocity gauge.
