D.C. Mun. Regs. tit. 9, r. 9-160
Statute of limitations. If the statute of limitations applicable to refund claims and assessments is open with respect to a particular member of the combined group, the statute of limitations is open with respect to that particular taxpayer notwithstanding the fact that the statute of limitations may have expired for one or more other members of the combined group.
The statute of limitations applicable to refund claims and assessments for members of a combined reporting group which have filed their tax return based on a fiscalized reporting period matched to the accounting period of the designated agent shall be the statute of limitations determined and computed based on the fiscalized accounting period.
If a return is filed pursuant to a combined report, the Chief Financial Officer may examine and audit that return, and collect any deficiency from a combined group member for whom the statute of limitations for assessments has not expired, even if the statute of limitations for other members which filed pursuant to the same combined report has expired. Any deficiency assessed pursuant to the audit or examination will not cause a reopening of the statute of limitations for those other members for which the statute of limitations has expired who filed pursuant to the same combined report.
D.C. Mun. Regs. tit. 9, r. 9-160