New bike or 2nd hand?
Sometimes these things matter little with Campag, as parts are shared among several groupsets and the finish & nuts & bolts may be better on the higher spec group.
Likelihood is that Mirage may have more steel chainrings than Veloce, that might be it.
But to the point in hand, if the bike was sold as "full" Veloce groupset then it obviosuly isn't. MTB's have often been sold with the description of "XT" compnenets when all they mean is the rear mech!