From my experience, that is correct. You can only un-merge compositions you have made yourself manually.
Unfortunately, identical composers and titles is not a safegaurd against roon miss-identifying compositions. Roon will simply misidentify both of them. I have had examples where roon has misidentified a dozen or more compositions but merged them all together because the titles and composers are identical.
Like the OP I find roon merging compositions incorrectly to be rather common. Several on this forum report this regularly. Some composers are more prone to this problem than others. The root cause is that a simplistic composition identification around opus numbers simply will not work in many cases. There are too many exceptions to this rule. In many cases it will go unnoticed in your library unless you have the habit of comparing interpretations or creating playlists with more obscure “covers”. Just a few examples:
- Debussy
Debussy did not use opus numbers. He was only cataloged in 1977 by Lesure, which Lesure completely revised in 2003. Metadata with any combination of no Opus or L numbers, English or French titles, one or other, or both of the L numbers is extremely common. This leads to a lot of randomness and mistakes in roon’s composition identification process for Debussy.
- Telemann
Telemann’s output was vast. It is rather hit and miss how “clean” the cataloging is in roons metadata sources. In particular, the TWV numbers are case sensitive so that TWV 43:g2 is different to TWV 43:G2. I find it extremely common for the case of catalog numbers to be mixed up and for roon to rather randomly group Telemann compositions.
.
3. Almost all the Russian romantics
All the famous complete ballets have “suites”, sometimes 3 or more, I find it extremely common that roon mixes the ballets up with the suites or mixes different versions of the suites and so does not group the compositions correctly.
Once roon has grouped compositions incorrectly, it is quite difficult to ungroup them.
a) You can try cutting and pasting the canonical names from allmusic and also adding WORK/PART tags to the multi-part compositions. Sometimes this works.
b) Often though you just have to start all over again and re-import. In this case, move the album somewhere roon is not looking. Roon will remove he album and its compositions from your library. Then “clean library” so roon has no memory of your album. Perform the edits in a) with an external tagger. Re-import the album and roon will usually identify your compositions correctly and group them differently.