The N stands for Nils Landberg, the U for uncut (smooth) glass.
This table I have had for years you may find it useful in the future:-
Art glass produced in a single, unique piece. Signed by the artist.
(Until 30th June, 1998, stood for Épreuve d'Artiste.) Art glass objects made in very short runs comprising a maximum of five pieces. Signed by the artist.
Orrefors Gallery collections are produced in limited runs of between 15 and 60 pieces. Signed by the artists. Several Orrefors artists are normally represented in each Gallery collection.
A new art glass category introduced on 1st July, 1998. Runs are as for Gallery, i.e. between 15 and 60 pieces, but do not form part of a collection.
Art glass made in a predetermined run of at least 100 pieces.
The following two tables show the meaning of the lettering in Orrefors numbers:
Initial Designer Initial Designer Initial Designer
A Olle Alberius H Edward Hald P Sven Palmqvist
B Gunnar Cyrén J Jan Johansson R Carl Fagerlund
D Ingeborg Lundin K Henning Koppel S John Selbing
F (Karl) Edvin Öhrström L Vicke Lindstrand T Lars Hellsten
G Simon Gate N Nils Landberg V Eva Englund
(NB: From 1980, two initials have been used, e.g.: NL = Nils Landberg, BB = Gunnar Cyrén)
Initial followed by letter A for cut glass
Initial followed by letter E for frosted glass
Initial followed by letter U for uncut, smooth glass
Initial followed by letter Z for green iridescent glass
Initial followed by Graal-S or S-Graal for Slip-Graal