According to experts it affects above all the marbled Montblanc writing instruments, such as the 333 ½. In 2004 such pieces were worth from around 500 euros upwards, which makes the effort worthwhile for counterfeiters. Fakes have already been sighted even among the inexpensive models, among them a pink Monte Rosa.
Since several thousand euros are quickly asked for old writing instruments, one should make certain before the purchase that the version offered ever existed at all. Picture comparisons with verified originals are helpful, as is the relevant collectors' literature, in which the model variants are documented. The basic rule is: do not buy writing instruments whose model history you do not know. There are more fakes than most buyers suspect.