Track header question

Here's a question: do you know what "Can.1" means exactly?

I opened a very old session and I noticed that some of the tracks have a "Can.1" written right next to the track name, on the track header space. It's written in grey and you can't modify it in any way..in other words it's always there, no matter what name the track has. I also noticed that the tracks which have that "Can.1" are the ones which are using sounds from an old library (I kept the library from the previous Garageband in my computer). I guess it somehow indicates that the sound is from an older library, but the problem is...if I change the sound, selecting one from the newer library, then I'm not able to go back to the previous one because I don't have it in the side menu. Do you know how to access that same old sound for example in a different session? As I said, it doesn't show on the side menu on the left: I only have it when I open the old session. Thank you so much for your help and sorry for the long question!