No. These plastic tubes are not retail packaging at all; they serve solely to send writing instruments to and from repair. One will therefore be in circulation for no better reason than that a genuine pen was once sent in for service, and any other pen can be slipped into it afterwards. As evidence of authenticity they are worthless; originals are supplied in a case or in the familiar outer box.
What counts is the pen itself. The cruder fakes from Far Eastern production, which cost a euro or two new in their country of origin, give themselves away unmistakably to anyone who knows what to look for: the star, the clip, the engravings and the standard of finish. It also helps to name the writing system correctly. If a rollerball is being offered as a ballpoint and the model cannot be traced in the Montblanc range at all, that is a clear warning sign. A seller's tale of the pen having once been repaired in a Montblanc shop is no substitute for proof.