In the spirit of “more and better edit notes” as discussed in another thread…
The blues duo Sonny Terry & Brownie McGhee performed and recorded together for many years. At some point in the past, all their releases were recredited to Terry & McGhee as individuals. I’ve recently started moving those back to the duo (as in this edit).
What would be a meaningful/useful edit note for a case like this?
My answer would be - I write notes expecting a total stranger who doesn’t know me to read it in five years time. I need to be clear to someone in the future that I did know what I was doing at the time. And they can trust my edit as genuine. I want to give them a good feeling that I actually checked my resources and know what I am talking about. I don’t want to them to think I just Google’d it, or stuffed a date in as I wanted a tag filled in.
I’d also try and make the comment readable and not just shorthand. A large number of the users will not have English as a first language meaning some details get lost.
With the example you have posted I don’t know an answer. My first is a question as you are changing two separate people into one entity which seems weird to me. So that becomes the answer… why are you making a single entity out of two separate people?
So that comes down to a edit note of “These two artists perform as a duo”.
Your note is close, but the meaning is a bit vague as it can be misread. I’d waffle it out a bit more into a clear English sentence. 
How about: “These two artists perform as a long-standing duo that’s considered by most to be a separate entity from their solo careers.”
Exactly like Lester Flatt & Earl Scruggs is handled in the database. The long standling duo comprising the individual artists Lester Flatt and Earl Scruggs. I’m sure there are many others.
Yes, there are many precedents - Simon and Garfunkel, Daryl Hall & John Oates, DJ Jazzy Jeff & The Fresh Prince, etc. There are even forum threads discussing some of these, so I don’t expect the recrediting to be controversial.
It’s easy to think “this is obvious” and put in some sort of minimal edit note, so I was looking for perspective on what might not be as obvious as I think (like @freso’s suggestion in the other thread of referencing the generating software when adding disc ids).
I wonder if it might be worth adding something to the guidelines regarding duos, for instance formalizing some of the points raised in the Jazzy Jeff/Fresh Prince thread.