All the yarns I have were purchased from villages.
I've never manually cut a yarn and have always relied on the automatic cutting to required length whenever I dry food or make blunt arrows.
When I do dry food that requires less than 25 feet of yarn and I don't have the exact length of yarn required, I'll try to use available yarns that total the length of cordage required.
For example: I need to dry 48 pieces of meat. I'll use the available 20 foot yarn of any material, plus a 4 foot yarn of any material.