Hello and warm welcome to the forum first. Congrats for your learning path so far and thank you for bringing this issue to the light.
Since I’ve seen questions about this here and there on this forum (a week or two ago there was almost the same question raised in another thread) I presume I’d need to include somethng about this in my “useful how to” thread too no matter it was originally aimed to mostly explain things about the forum. I’ll do this later on.
And, yes, this is the matter of New VS Old material. The indicator besides the music can also be that the old courses are named “Course” (1, 2 and 3) and the lessons in them are “Lessons” (1-25 usually) and the new courses are named “Level” (1,2 and 3) and the lessons in them are “Challenges” (also 1-25 usually although Level 3 is not entirely finished yet).
Hoep it helps.
Pob lwc ac dal ati! (good luck and keep going)
Hwyl!
Tatjana 