Rathbone's is from a recording of the Red-Head league, it's when he was older in 1966 for Caedmon Records, and I think it's a audio book or radio program. So the movie is taking place during The Adventure of the Red Head League, because it's one of the few times we see them go to the theater to listen to music. However there is one thing that could cause this to be an issue, although not really unless you over analyze this. So Laurie Main, who voices Watson, since they couldn't use the Nigel Bruce lines from the 1940s movie because they would sound so different, had his lines come not from any main Sherlock story, but rather from a CBS TV kids show series called CBS Mystery theater.
In this case CBS took the story of The Treasure of Alpheus T. Winterborn, a kids novel by John Bellairs and illustrated by Judith Gwyn Brown and is part of the Anthony Monday Series, and converted it into "The Clue According to Sherlock Holmes" which used him as a narrator to tell the story of Anthony Monday's case.
https://johnbellairs.fandom.com/wiki...herlock_Holmes
The line in question I think about the music being "frightfully dull" comes from early on when Holmes is practicing his violin and Watson is playing a jigsaw puzzle.
So There you have it, it's taking place during the Red Head league, and the two lines are from vastly different locations.
PS. Basil of Baker street has 5 originals and 3 new ones that started in 2018. Also the name Basil is connected to Holmes in a way before Basil Rathbone took on the role of the great Detective. Anyone know what that connection is?