Hi amc! Yup, it is not uncommon for old CO and CA accounts to pop up.
I would always, as a first step, validate the debt and when it occured. Dig out your records, with specific emphasis on locating the date of default of the debt. Validation by the CA or OC can also be obtained by a DV or HIPPA process under the FDCRA, which may be required if you cannot validate it yourself. Dont call them! All certified mail. I would not pay a penny until all validation is completed to your satisfaction. I also would not pay until I had first attempted to get a PFD agreement from them, for simply paying without a PFD wont get it out of your CR.
Regardless, you must obtain the DOFD, which is the first date in the last chain of delinquencies on the default account. The delinquency cannot continue to appear in your CR, by law under the FCRA, for more than 7 1/2 years from that date, regardless of when it was placed as a charge off or collection, or whether you have made any partial or full payments.
As a separate matter, the SOL also runs from that default date. Add your state SOL to that date, and that tells you the date after which they can no longer obtain a court judgment on the default. It has nothing to do with your CR, but is important to know in the legal process.
Good luck!