Extra set of Cords: Double the standard number of elastic cords.
The standard number of cords is 10. You can purchase and extra set to upgrade to 20, if you think that your usual number of scores in a concert will be more than 10.
This does not increase the size of the folder; the extra cords are simply affixed along the existing notches in the hinge so that each of the original strands becomes a double strand. The cords are like tiny Bungee® cords, with many rubber lengths encased in a woven synthetic sheath. They're strong and durable, and thick enough to avoid tearing music.
Singers can use multiple cords to hold a larger masterwork in their folder (and...pro tip...strategically placed, to jump between sections).