I had a Eureka tent for over 20 years. The shock cords outlasted the tent.
I use an REI tent now and had to replace the shock cords after 2 years. The new cords seem to be fine after 5 years. I wish I could remember what kind of cord I bought.
All shock cord is not created equal.
EDIT: Holy crap I actually found the good cord I bought years ago. It's lasted quite well:
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https://www.ebay.com/itm/16649236907...UAAOSwvghd~6f0