This is a good point. I think it shows how the wording of the guideline might be improved.
I interpret, "only the most prominently featured names need to be included" as meaning, "the most prominently featured names must be included, less prominent names not not have to be included, but they can be… and maybe should?". Changing one verb would convey your intended meaning more clearly to me: "only the most prominently featured names should be included"
Fair enough. But common sense is not so common (either in the sense of "frequently found", or "widely shared"). And what the guideline offers now is silence. It's possible to write words that convey flexible guidelines. Something like, "Usually no more than three to five, but maybe more if this factor and that factor." Or, "Brevity is good, and including the most important contributors is good, strike a balance."
You know, I don't see the concept of "should be added as credited" anywhere in Style / Classical / Release / Artist. Adding words to that effect would be helpful, I think. How about, at the start of Featured Release Artists, add a second sentence which reads:
In the "Artist as credited" box, fill in the name as spelled or abbreviated on the cover, e.g. fill in last name only, if the cover includes only the last name.
I think it would be helpful to add comments to each of the guideline's examples pointing out how the wording on the cover led to the wording in the Release Artists string.
Does the example, "Début Recital Martha Argerich" demonstrate a guideline that "only the most prominently featured names should be included"? The less-prominent names of Chopin, Brahms, Liszt, Ravel are left off.
Would it be helpful to add the Matthäus-Passion by Bach; Nikolaus Harnoncourt as an example of both leaving out less-prominently featured names on the front cover, and crediting names as on the cover (last name only for "Bach", full "Nikolaus Harnoncourt")?
By the way, one example is: "Copland Conducts Copland Aaron Copland; Aaron Copland, London Symphony Orchestra, Columbia Symphony Orchestra, William Warfield". That's now a bit stale: in the live Release entry, the composer credit no longer includes the first name "Aaron". I'm not sure why the performer credit includes the first name, because the cover says "Copland conducts Copland", last names only.
It might be that these wording improvements to the Classical Release Artist style guideline might be editorial only, and would be quite a bit of help. I'd be glad to offer first drafts of such changes.