So I think you have solved this issue but it raises another question how can I see the actual number of discs now if I continue use this solution?
I am not sure. Someone else might know.
One way that might work for you is to note the number of albums reported in the album pane (Value A). Then create a smartlist with this expression.
[Media Type]=[Audio] ~nodup=[Album Artist] ~dup=[Album] ~nodup=[Album]
(If you have not set [Album Artist] you can probably use [Album Artist (auto)] instead. I do not think more than two various artists albums with the same album name will be picked up by this method.)
Note the number of files reported (Value B).
Then add ~nodup=[Album] to the smartlist expression like this:
[Media Type]=[Audio] ~nodup=[Album Artist] ~dup=[Album] ~nodup=[Album]
Note the number of files reported (Value C).
Manually calculating B-C+A should give you the total number of albums.
If you want to know how many discs those albums contain perhaps you can use a similar successive smartlist method with Disc#.
But I am sure that someone else has an easier method to offer.