Brian,
My apologies: I don’t think I understand your question 
.
If you’re concentrating on anomalies specific to the way Roon handles ‘Classical’ music, you have probably revealed the difference (control over which Roon is surely hopefully still developing) between the way that ‘Classical’ music prioritizes the composer then the composition; whereas other genres seem (as far as I can tell - not my field) to identify by artist then ‘item’, which seems always to be called a ‘song’, regardless of whether or not it is actually sung.
My assumption would be that - unless Roon is correctly deriving a unique ID tag for Brahms Op. 51/1 - it may not be finding others in your Library because they are named differently… ‘Opus’, ‘I’, ‘No.’, ‘No’, ‘Number’ etc.
Does this thread help - particularly this explanation from Suedkiez?
The disc icon and number shows how many known recordings of this composition exist, including streaming… The book icon and number (which you can click as well) shows how many of those recordings are in your library.
…I was able to get one of the recordings to show up, but only after manually adding the work and part tags in mp3tag:…
That’s OK and to be expected. If you use Yate for tagging, you can have it batch split the Title field into Work and Part (semi-)automatically - and in accordance and full compliance with what Roon expects.