The law taxes income, not pieces of paper.  Is this the only reason filing of the return is delinquent?  File the return with the correct amount of UC received.  IRS does not send a bill.  It sends a letter (usually a CP2000) proposing an assessment.  Make sure your client answers it promptly.  It would help to attach an explanation to the original return.  IRS won't look at it when the return is filed, but they might see it when the document matching is done.  Otherwise, you just have to send them a copy of the explanation you have already submitted -- and maybe by then, a copy of the corrected 1099-G.