Yes, for a long time the 149 was supplied with 14-carat gold nibs. According to collectors, the change to 18 carat throughout coincided with the alteration in nib design: older nibs show a large platinised centre, later ones only a narrow platinised band. That change is dated to the early or mid 1990s, though not documented to the day. Fourteen-carat nibs are accordingly found on examples from the 1980s and before.
The dating is not purely a matter of chronology, however, since the fineness also depended on the country a pen was destined for. Pens for the French market, for instance, always had 18-carat nibs, so older 149s with 18 ct turn up there as well.
A 14 ct nib is thus no defect, and certainly no cause to doubt authenticity; it is a mark of age. In dating a 149 it should be considered together with the nib design, the cap-ring engraving, the feed and the form of the piston mechanism, since only the combination of these features allows a dependable placing.