The two ranges are often confused, dealers included. The surest distinguishing mark is the end of the clip: SlimLine writing instruments always carry a plastic star mounted there, Noblesse ones do not. The SlimLine sat below the Noblesse, was considerably cheaper and had no genuine gold nib; it is considered neither rare nor worth collecting.
The Noblesse of the first series, the Noblesse I, by contrast has a 14 carat gold nib. Its last shop price was 98 DM. Valuations on the collectors' market are correspondingly modest. The slim design stayed in the range for a long time, so pieces from the late 1970s are no rarity.