When an appellate remand results in modification of a felony sentence during the term of imprisonment, the trial court must calculate the actual time the defendant has already served and credit that time against the “subsequent sentence.” On the other hand, a convicted felon once sentenced, committed and delivered to prison is not restored to presentence status, for purposes of the sentence-credit statutes, by virtue of a limited appellate remand for correction of sentencing errors. Instead, he remains “imprisoned” in the custody of the Director of Corrections “until duly released according to law,” even while temporarily confined away from prison to permit his appearance in the remand proceedings. Thus, he cannot earn good behavior credits under the formula specifically applicable to persons detained in a local facility, or under equivalent circumstances elsewhere “prior to the imposition of sentence.” Instead, any credits beyond actual custody time may be earned, if any at all, only under the worktime system separately applicable to convicted felons serving their sentences in prison. Because this defendant is a Three Striker, he has an indeterminate term and is thus ineligible to earn such prison worktime credit for the time between his initial (error plagued) sentencing and his resentencing following remand.