Look up legal actions taken on this company, you may be able to use that as leverage to get the CA removed as they are also bound by legal settlement. If you cannot use the consent decree then you would have to use GW letters to the CA asking that it be removed.
The issue would be whether the debt collector had legitimate collection authority at the time they reported their collection.
The fact that the OC is no longer in business would not negate the fact of their prior referral or sale of the debt, thus providing collection authority to the debt collector.
I dont see any relevance to accuracy of the debt collector having had collection authority, and thus the legitimacy of their reported collection.