In United States v. Mitchell, the Sixth Circuit addressed cross-appeals from a grant of habeas relief under 2255 based on the inapplicability of the Armed Career Criminal Act. Mr. Mitchell was resentenced at the district-court level, because he no longer qualified as an armed career criminal. Because he had already served a seventeen-year term of incarceration, more than the maximum sentence that applied to him without application of the ACCA, the district court imposed a sentence of "time served" and released Mr. Mitchell.
On appeal, the Sixth Circuit reminded the parties that "this precise issue" had already been decided in United States v. Nichols, 897 F.3d 729 (6th Cir. 2018). In Nichols, the Sixth Circuit held that a time-served corrected sentence is unlawful, because it makes the length of actual incarceration served the length of the sentence imposed, even though that amount of time is beyond the applicable Guideline range and often beyond the statutory maximum sentence available. The Court also took pains to point out the four different options available to a district court in habeas: 1) discharge the petitioner, 2) grant the petitioner a new trial, 3) resentence the petitioner, or 4) correct the sentence.
A corrected sentence is subject to reasonableness review. But interestingly, a full resentencing is not needed. Instead, the district court may "impose a corrected sentence based on a brief order, a hearing that resembles a de novo sentencing proceeding, or anything in between." Mitchell (quoting Nichols at 738). In other words, not ever habeas revision of a sentence requires a full resentencing - and what degree of corrected process is required is based on the individual situation at hand. It is also a matter of judicial discretion.
It is worth noting that Mr. Mitchell also attempted to challenge his three-year term of supervised release, presumably because he served additional time beyond the lawful sentence. However, the Sixth Circuit declined to address the question in light of the remand. Instead, it directed the district court to "take the opportunity to provide an appropriate rationale for its supervised release decision."