Singers/artists and their various bands - all separate entries?

Costello happens to be the example used in this guideline:

Where a band is credited in the form 'Bandleader and The Musicians' (Elvis Costello and the Attractions, for instance) they should be credited that way and will have an entry in the database all of their own. It's possible, though, that in other titles they'll be credited separately or independently. If either Bandleader or The Musicians appear somewhere on their own, we could end up with an entry for 'Bandleader' as well as one for 'The Musicians'. So, we have a page for Elvis Costello on his own as well as one for Elvis Costello and the Attractions. So far, we have no page for The Attractions, but if they ever get a qualifying credit on their own without Costello we'll create one. As long as they are credited on screen that way, this is fine.

To add to Peter's posting but from my contributor POV, I add credits based on the onscreen credits, If it said 'Metallica' I'd add that but not any members unless they were also separately credited onscreen by name and viceversa. I'll always match what is onscreen and if the band does not have a page (which is rare) I'll create one.

Now I get what you're saying about the less obvious ones and if the duet is just the peoples names with 'and' between, I'd add as two name pages, if they have a name for the pairing and it's be a rare one off entry for like a one off song, you could get away with adding the real names and other duet name as an attribute for both if it reflects what is shown onscreen and their real names aren't used.

It's always worth cross referencing onscreen credits with other sources, then you can make a choice on what to name the page. Like if a band was credited onscreen as 'Wiggins' but every other legit source/music releases called them 'The Wiggins', you obviously go for longer title and (as Wiggins) attribute.

If it looks good on the site, is accurate onscreen info and within guidelines, I just do it.
Also if I create a band page, I add some info to it including [link=???]'s to the band members pages in the trivia so it helps identify the page as well as provide some info to users. As I think, every good honest contribution improves the site in some small way.
Sorry if I sound like I'm teaching Granny how to suck Apples, I'm just explaining my thought process on the topic rather than instructing anyone on things they already know,

About.. ”If it said 'Metallica' I'd add that but not any members unless they were also separately credited onscreen by name and viceversa.”

You can (it’s listed in the guide, btw) add the confirmed members/musicians with ”(uncredited)” atttribute. If I understood the guide correctly, you could add them as:

Ulrich, Lars … Self - Metallica … (uncredited)

Personally I believe that the person’s name is more important than the band (ideally, both are added), since there can be different members in the band through the years, substitute musicians etc.

I was basically referring to some bands/groups e.g. performing on stage and only the name of the band/group is credited (which is actually often the case with tv specials, award shows, live performances, etc - they don’t always credit all the musicians).

If I can identify all (or at least some) the members of a group like (random example) ”Gipsy Kings”, I could add them with ”(uncredited)” attribute. Usually all the band members are visible during the live performance. At least in some shots.