That’s pretty much how my multi-disc albums are organized, and it fits with Plex’s strategy, as well as MusicBrainz’. Plex would normally organize these sets as a single album with multiple discs.
However, the OP doesn’t want it that way. He wants each disc in the set to be treated as a separate album. But I think it’s going to be very difficult to force Plex to go against that strategy.
Since the re-write of the Plex Music agent last year, I have found it to be dramatically more accurate and dependable than the old agent, if your embedded tags are in order AND your media is organized the way Plex prescribes. Paradoxically, while the new agent is better at using embedded tags, it is also more dependent on the folder structure/filenames than the old agent. I have lobbied to change this, because it doesn’t make sense. Hopefully someday we’ll get there, but that’s the way it is for now.
I’ve found that trying to impose a different organization, like separating multi-disc sets into separate albums, on Plex is extremely difficult. It causes the matching functions to be unpredictable, giving illogical results like the one @northrwl has described.
@northrwl, the only thing I can suggest that might get you closer to what you want is to use the ‘fix match’ option and select the ‘Personal Media Artists’ agent.
