I'm sorry, but I'm not a professional plumber...
It sounds like you're going to have the burden of proving that it did have the ferrule on it...but I think that you know what. When a product is installed outside of the manufacturer's guidelines/instructions, you'll likely not obtain performance information. If they tell you that it will last exactly three years and one month, then now they're liable when it fails at three years and zero months.
My question for you is, at those pressures, why did you not install a PRV? Water under the bridge...I know.
Also, it sounds like your plumber (buddy or not) would be the one liable for this mistake...it should be his burden of proving that he placed the ferrule on the pipe. At a minimum, he should pay your deductible. If he canceled his insurance, the question is would it be covered now if he did the work when the policy was active? Dunno.