Plex media server not finding music

Hi Guys
this may be a complete lamer question but I have several albums on my plex server where plex only finds one album is there,
an example would be Nick the Night fly album, I have 15 albums (2cds each) all in Nick the night fly folder - when I look in media server it sees only one album.
Many thanks
Roy

Music requires, unfortunately, pretty right adherence to the naming rules.

I have, after passing through MusicBrainz “Picard”, the following structure

Artist/
  Album/
    Disc n/  (if multiple discs only)
      01 - title

As example:

[chuck@lizum Dan Fogelberg.105]$ ls -R
.:
Dan Fogelberg - Greatest Hits/  Dan Fogelberg - Portrait: The Music of Dan Fogelberg/
Dan Fogelberg - Home Free/      Dan Fogelberg - Promises/

./Dan Fogelberg - Portrait: The Music of Dan Fogelberg:
Disc 1/  Disc 2/  Disc 3/  Disc 4/

./Dan Fogelberg - Portrait: The Music of Dan Fogelberg/Disc 1:
01 - Part of the Plan.mp3    07 - Same Old Lang Syne.mp3  13 - Lonely in Love.mp3
02 - The Power of Gold.mp3   08 - Run for the Roses.mp3   14 - Rhythm of the Rain.mp3
03 - Heart Hotels.mp3        09 - Make Love Stay.mp3      15 - Magic Every Moment.mp3
04 - Longer.mp3              10 - Missing You.mp3         16 - Don't Lose Heart.mp3
05 - Hard to Say.mp3         11 - Language of Love.mp3    cover.jpg
06 - Leader of the Band.mp3  12 - Believe in Me.mp3       music Dan Fogelberg Disc 1.m3u

./Dan Fogelberg - Portrait: The Music of Dan Fogelberg/Disc 2:
01 - To the Morning.mp3           11 - Sweet Magnolia (And the Travelling Salesman).mp3
02 - Stars.mp3                    12 - Windows and Walls.mp3
03 - Wysteria.mp3                 13 - Seeing You Again.mp3
04 - Song From Half Mountain.mp3  14 - Bones in the Sky.mp3
05 - Old Tennessee.mp3            15 - The Minstrel.mp3
06 - Nether Lands.mp3             16 - Mountains to the Sea.mp3
07 - Scarecrow's Dream.mp3        17 - A Love Like This.mp3
08 - Since You've Asked.mp3       cover.jpg
09 - Hearts and Crafts.mp3        music Dan Fogelberg Disc 2.m3u
10 - Only the Heart May Know.mp3

./Dan Fogelberg - Portrait: The Music of Dan Fogelberg/Disc 3:
01 - Tullamore Dew.mp3       07 - Wishing on the Moon.mp3  13 - The Wild Places.mp3
02 - Phoenix.mp3             08 - Empty Cages.mp3          14 - Democracy.mp3
03 - As the Raven Flies.mp3  09 - The Innocent Age.mp3     15 - A Voice for Peace.mp3
04 - The River.mp3           10 - What You're Doing.mp3    cover.jpg
05 - Once Upon a Time.mp3    11 - She Don't Look Back.mp3  music Dan Fogelberg Disc 3.m3u
06 - Tell Me to My Face.mp3  12 - Aurora Nova.mp3

./Dan Fogelberg - Portrait: The Music of Dan Fogelberg/Disc 4:
01 - Nexus.mp3           07 - The Reach.mp3                  13 - River of Souls.mp3
02 - Illinois.mp3        08 - Tucson, Arizona (Gazette).mp3  14 - Ever On.mp3
03 - The Last Nail.mp3   09 - Go Down Easy.mp3               cover.jpg
04 - Dancing Shoes.mp3   10 - Sutter's Mill.mp3              music Dan Fogelberg Disc 4.m3u
05 - Paris Nocturne.mp3  11 - Song for a Carpenter.mp3
06 - Beggar's Game.mp3   12 - Forefathers.mp3

./Dan Fogelberg - Promises:
01 - To the Morning.mp3      05 - Song From Half Mountain.mp3  09 - Old Tennessee.mp3
02 - Part of the Plan.mp3    06 - Leader of the Band.mp3       10 - Promises Made.mp3
03 - Souvenirs.mp3           07 - More Than Ever.mp3           Promises.m3u
04 - Looking for a Lady.mp3  08 - Comes and Goes.mp3
[chuck@lizum Dan Fogelberg.106]$ 

Here are some tips regarding music

multi-disc albums
https://forums.plex.tv/discussion/comment/1050849/#Comment_1050849

handling singles and EP’s
https://forums.plex.tv/discussion/comment/1093611/#Comment_1093611

possible ‘side car’ files for music
https://forums.plex.tv/discussion/comment/1319703/#Comment_1319703

soundtracks and ‘various artists’
https://forums.plex.tv/discussion/comment/1472799/#Comment_1472799