Really helpful, Tony 
I understand and follow everything you say. Thanks.
GIGO: if the metadata is poor online, I can see how Roon cannot be expected to ‘improve’ on it .
Is there any way to know (for sure) when Roon has ‘failed’ to make an accurate match with AllMusic?
I’m already planning it. I shall split up the 200 Albums which I have stored in Roon, accumulated over three years or so, and edit them in batches. A long job. But my uses, as you say, will be the better for it.
What’s been misleading me, I think, is an assumption from posts like this one of mine three years ago (in which you were good enough to help as well, Tony, thanks!) that Roon could do more than I thought it could: “Just import a file and Roon will do the rest”.
I have a lot invested in Roon and want to make the most of it.
Your help, guidance and suggestions: INVALUABLE. Thanks so much again .