These are already well tagged. Albums in individual folders, complete tags such as Artist, Album and Title.
Nevertheless, Picard often does not find a matching release, although they are present, or assigns them to wrong releases, although the number of tracks or their names do not fit and would fit in other releases.
I have the impression that Picard is a powerful tool, but I find it rather frustrating to get started. At first I would like to make it very simple and find the matching releases by artist, album, title, number of tracks (and year if available).
As a next (optional) step, I would like Picard to help me select the correct medium (CD or vinyl) if this is already stored in the folder name or tag.
Do NOT try to tag 100,000 files in one go. Create a new directory for the tagged files and let Picard move your files into the new directory when it saves the tags.
Take a copy of a small subset of your files to test Picard on first (so that if they get screwed up because e.g. you made a mistake in your file naming script, they are only copies and not original files. Once you have tweaked Picard settings to work in the best way for your music collection, then load files in batches of (say) 50 albums (which is going to be c. 1,000 files) and once you have saved them you can remove the releases from Picard (which doesn’t delete the files) and load the next batch.
In my own experience it is normal to have to select a different release for some albums. However by tweaking the settings in Options/Metadata/Preferred Releases you can give Picard some strong hints about the types of music you have i.e. prefer CDs or Vinyl or Digital downloads, prefer albums, prefer specific release countries etc. There are also some settings in Options/Advanced/Matching that might help get the exact matches right even more often - however you should still expect to find some mismatches.
Even with half decent existing Metadata and optimum settings, Picard sometimes selects the wrong release. (If you can collect details of what search Picard does from the Debug/Error log and put them in a thread here, maybe someone will try to work out why and improve it for next time.) So be prepared for this.
Start using Cluster/Lookup which tries to use the existing tags and directory/.file names to find the right release - but Picard is going to have to make a guess at this stage. If you get the wrong release selected you can: Right click on the release and select alternative releases from the same Release Group; or use Search to get Picard to make a manual search of MusicBrainz and select the release; or use Scan and see if using the scanned AcoustID improves the release choice.
When you save releases in Picard, it includes the MusicBrainz IDs (MBIDs) in the tags that are saved, and when you reload the files into Picard again, it thus knows exactly which release to load from MusicBrainz. So manually tweaking the release is a one-time activity.
FINALLY…
AFAIK, there is no way as standard to use e.g. the text “CD”,“LP”,“Digital” etc, in path/file names to tell Picard which type of release to prefer, and from my knowledge of plugins I am not sure whether there is scope for a plugin to be able to do this either. Philipp / @outsidecontext may have a better idea of whether this is possible or not using a plugin or whether we could enhance Picard to search for and use such data for searching.
One thing to add to @Sophist is backup your collection before you start. Throw the backup in a drawer and keep it safe. Then if you find something has miss-fired during your mission your have a reference to return to.
I know that I have to check the results and that Picard cannot make the correct assignment in all cases.
But not even in those cases that seem simple to me as described above?
If I have understood correctly, it is not unusual for Picard to recognize a release incorrectly (for example, assigning an album with 11 tracks to a release with 9 tracks, even though a release with 11 tracks and matching titles is available / or not recognizing a release, even though all the necessary information such as artist, album and title is available and the corresponding release is available)?
Is there no way to set Picard so that it adheres to these simple principles (matching artist, album, title and number of tracks) or favors them over others?