Such transitional combinations actually occur: on model changes, Montblanc occasionally fitted remainders of predecessor nibs in the successor models, so e.g. early 149s with 139 nib or 146s with 136 nib turn up in collections. Feeds were partly later exchanged in service for the round models from the 1950s. Such a combination mostly does not increase value, since it is not model-faithful; some collectors even rate the mix as value-reducing. More frequent are, however, subsequently swapped wrong nibs on the market, which is why on purchase special caution is warranted.