Coastie, Aardwolf,

The lenght of cord is a first guess based on another item "waved" using the Slatt's knot.
Maybe it will be 2 x 13meters vs 26 meters... don't know for sure right now.
So the length's difference is not really an issue.

Like both of you, I too think 13 or 14 meters is quite a good piece of cord and should cover enough possibilities.

OTOH, I like to hear other's opinions....

By the way, I don't envision rapelling down a 20 (or more..) meters frontage/cliff, using a mere paracord.
OTOH, if I really have to, 14 meters, with two pieces of paracord... well... there always is a first time, no !?

I like those Darwin Awards "famous last words" :
"It seemed like a good idea at the time"