This guideline refers incorrectly to Paul McCartney.

He has a Member of the British Empire award which entitles him to use the letters MBE after his name.

Separately, he has been knighted by the Queen which entitles him to use the title Sir before his name. (The guideline says he's never referred to as Sir but he is on https://www.amazon.com/Garland-Linda-Commemoration-Life-McCartney/dp/B00003ZKRB for example). If she ennobles him he will become Lord Paul McCartney.

My suggested corrected Guideline section is:

Definite articles and titles

Only include definite articles (like "The", "El" or "Der") when used by the artist as part of the name. Do not generally use honorary titles (like "Sir") as part of the artist name stored in MusicBrainz. The same approach applies to letters after the name. These may be added at the "credited as" stage.

Glenn Miller Orchestra doesn't have an article on their official name (but In the Nutcracker Mood is credited to "The Glenn Miller Orchestra").
Paul McCartney is knighted, but should only be "Sir Paul McCartney" when recorded or listed as such.