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The balance on the revolving account, and thus its effect on % util, is the same as that of any other revolving account. The CO is a tack-on that remains unless they voluntarily delete the reported CO. Reduction of % util on one account normally, but not always, improves % util. Paying down a maxred out account will almost always improve your % util scoring, but if all accounts, for example, are reporting $0, that is not maximization of % util.
If you pay off an account that was previously charged-off, I would suggest including the following logic in your GW request.
Reporting of a CO is basically placing a statement in a consumer's credit file that they are not expected to pay a debt. If the consumer does, in fact, pay the debt, it does not remove the fact that the creditor took that accounting measure, but it does show that the consumer does, when finally able, pay their obligated debt.
Thus, it can be argued that removal of that statement from a consumer's credit report more accurately reflect upon the commitment of that consumer to pay their obligated debt, and not simply continue to stiff their debts.