You would only be re-bucketed if that CO went away completely. I'm guessing that the dispute could have caused the initial drop. The final drop, assuming nothing else happened to your reports, could have been caused by the date change on the "reported date" or the DOLA to the day or month you paid the account. FICO is likely reading this as a newer baddie and that could very well do that. A "settled" account with that mention on your CRs is just as bad as a CO in lenders' and FICO's eyes.
You could GW the OC and ask them to remove those comments. Comments may include "charge-off", "settled", "settled for less than full", "was a charge-off" or the like.