The issue of whether to pay a CO is not restricted, for scoring impacts, only to your current status and credit report.
COs always have the potential of being referred or sold to a debt collector, thus potentially adding a collection to your CR.
Additionally, if the debt is still within SOL, they may obtain a legal judgment and report to the CRA.
Finally, aside from pure scoring issues, the presence of an unpaid, delinquent debt in your file will raise serious eyebrows upon a manual review of your CR.
Even after exclusion from your CR, a future creditor may simply ask if you have any old, unpaid delinquent debt. It might be a bit less than honest to reply "no" based simply on the fact that it is no longer being included in your CR.
In my opinion, it's always best, aside from the $$ out of pocket, to pay old, delinquent debt.
