REI's company "Policy" has NEVER been about the product. Their policy has ALWAYS been about the customer.
It is simply about the customer's satisfaction with their purchase. Period.
(As we all know) before they changed it last year, a person could walk into an REI with 20 years of heavily used stuff and claim that they were "Not 100% Satisfied", and they could expect a refund. (Like other former REI employees, I have many stories.)
Now, you have one year to beat up your stuff, bring it in, and claim you are not "100% Sarisfied." You paid for one years worth of total satisfaction. If you consistently show up at the return counter, it will be eventually noticed.
If you were genuinely not happy with the stuff and you get scoffed at, just tell the manager of the store that the CS employee you talked to probably needs their break just about now.
But the OP's issue is different. His REI BRAND bivy is now useless because the seam tape delaminated on its own. Given how long ago he bought it, this may no longer fall under the "100% Satisfaction Guarantee" anymore (but this is grey to me because he bought it when the old policy was still in place, so theoretically he could still claim he's not satisfied.)
But since REI manufactured it, it does fall under their "Limited Warranty", and it should ultimately be up to them to repair or replace it, not us BPL'ers. (BTW, please don't assume for a second that a custom repair of a bivy is less expensive for REI than a full replacement of the product.) The OP paid a whole lot more money for that bivy 20 years ago than it took to actually manufacture it, because he paid for REI's future support of the product and his loyalty.
Of course REI's final determination could obviously impact the future loyalty of a longtime customer, and they know this.
Aka: owner of a new "Dead Bird" jacket, thanks to a great company I'm loyal to, and numerous recommendations of many BPL's on this list