I know.
In the past there was set a rule that any research that is optional, would not require any chapter specific goods.
In this case it demands for the sheets of music.
Maybe to refresh your memory, chapter 16 Embassies wonders, union street, city expansion 49 don't need chapter 16 goods.
same goes for chapter 17, chapter 18 and chapter 19.
If memory serves right, this rule was put in place for players would skip some none required developments so they could go faster in to the next chapter, and later on they noticed they need to rebuild the chapter stuff again just to compleet those development they skipped.
And for my opinion, if you make a rule for a game you apply it to all the same situations in future expansions as well.
And that is what I am asking for in this situation as well.