I have no documentation of the shingles we had installed when we build our home in 1999. The shingles are falling apart, cracking, etc. and the manufacturer we believe made them is saying they aren't theres.
You don't and that's the plan. Even if you determined the manufacturer, they'd deny a claim by simply claiming they weren't installed correctly or, in your case, they'd still just deny they're theirs. And, the only way to even have "a chance" in forcing them to honor their warranty would be a lawyer, lots of money and even more time. Corporations (non-people) mean more than their customers (people) is the moral of the last century's story. A recall is just a super-cheap bailout to silence all of the preyed-upon victim whiners.
Even so, it's a 20 year old roof. Unless they were expensive 35 year shingles they have run the course of their life expectancy. In any event shingle warranties are prorated. Let's say the original shingles were rated for 20 year life span, which is pretty well standard builder quality shingles. Perhaps a 25 year warranty. Let's assume 25 years. The shingles have been on the house for 18 years. Assume the actual cost of the shingles new was 3000 (not labor, underlayment , flashing, ice shield etc, just the shingles because that is all the warranty covers) . The prorate is 18/25 (.72) . The amount the shingle company would credit toward a new roof is 3000 - (3000 x .72) or 840.00. You would need to pay the additional material and labor costs. If they were 20 year shingles the prorated amount would be 300 payable to you.