This Form 1099-R shows a nontaxable direct rollover from a qualified retirement plan. If this rollover was to an IRA, the IRA custodian will issue a Form 5498 reporting the receipt of a rollover contribution, so even if the IRA Automated Underreporting System flags the omission of the gross amount from Form 1040 line 5a, the examiner should recognize that the rollover was completed an not issue to you any notice of underreported income. However, some examiners are better than others, so they might question this rollover.
If the rollover was to another qualified retirement plan, no reporting of the receipt of the rollover is made to the IRS by the plan administrator. Even if the gross amount was present on line 5a, since such a rollover is less common than one to an IRA, the IRS often questions the completion of the rollover unless you included an explanation statement attesting to the fact that the rollover was completed to another qualified retirement plan.
In any case, it's probably not necessary to amend, but be prepared to provide supporting documentation to the IRS showing that the rollover was actually completed in case the IRS has any questions about this transaction.
