Reading also the JCT report on the CARES Act and the Senate Finance Committee summary on the COVID-Related Tax Relief Act again, it may even look like the limitation for offset to advance refunds in §6428A was deliberate.

In the summary for Additional Recovery Rebates Credit, it reads (emphasis added): Advance payments are generally not subject to administrative offset for past due federal or state debts. In addition, the payments are protected from bank garnishment or levy by private creditors or debt collectors.

In comparison, the JCT report says this about the Recovery Rebates Credit and advance refund (emphasis added): Any overpayment resulting from the recovery rebate credit or from related payments to the U.S. territories is not subject to reduction or offset by other assessed Federal taxes that would otherwise be subject to levy or collection. In addition, such overpayments are not subject to offset for other taxes or non-tax debts owed to the Federal government or State governments, except for certain claims for delinquent child support payments.

It is evident from the texts above that Recovery Rebates Credit is only mentioned in the JCT report on the CARES Act but not in the summary for the COVID-Related Tax Relief Act.