Boy, I just can't see how a brokerage firm could get a matured bond proceeds wrong. It's simply the face amount of the bond, right?
If you're really confident that you've got this all correct then one approach could be to leave the proceeds alone and use whatever basis figure you need to get your gain/loss properly stated. That does eliminate the possibility of the IRS's computers flagging the transaction as "proceeds don't match" and as long as you have your gain/loss properly stated the IRS can't really lay a finger on you.
