Hi I may have resolved this myself, but I thought I should report it in any case.
I went looking for my Karajan / Berlin 1981 recording of The Planets, but couldn’t find it. I checked iTunes and there it was - ‘Show in Windows Explorer’ and it’s right there in my watched folder.
Oddly, I have three Karajan planets - two copies of the 1961 Decca/Vienna version (one individual CD, and one from The Decca Sound box) as well as the Berlin. I think the duplicate filter is being a little over-zealous here, yet oddly inconsistent as it let through both Vienna recordings (that said, one of them has the Perfect Fool ballet suite on the same disc) while blocking the Berlin as duplicate - despite the fact it is a completely different recording.
Perhaps when deciding if an album is a duplicate it could look at the discs TOC, track timings and user-supplied metadata to make a more informed decision on whether an album is a genuine duplicate?
Easily resolved - I changed my settings to show duplicates, forced Roon to use my metadata (adding [Karajan-Berlin] to the album name, and now it’s no longer classed as a duplicate.