How is a Montblanc fountain pen to be assessed whose components come from three or four different epochs?

Such a fountain pen was never originally delivered in this configuration but assembled from parts of various models and epochs. A war-related makeshift assembly is unlikely if components from the 1950s are contained. Such a mixed piece is collector-worthy at most as a parts donor; a proper model attribution is not possible. On sale it should be declared accordingly to avoid false expectations.