Thanks for your fast and kind answer.
When I got albums (complete or not), I first cluster then look up and then scan when necessary. And it works fine in that case.
My issue appears when working on folder of unsorted, alone singles. A big part of them already have IDTags. But I observe "Lookup" does not perform good (got compilation instead of original artist album, or sometime wrong artist/title) when "Scan" is better (correct title/artist, but various artists compilation instead of artist album).
I'm not sure it is a buggy feature or a misinterpretation of the settings from my part
I would be interrested in such a plugin when you think it is ready for dispatch