why do you think you have to amend? if you entered these two forms correctly in the first place, everything should be correct.
Based on the form information you provided, what really occurred, is
1) you rolled over a 457 plan to a TRAD IRA at Vanguard (this is what the Code G on the first form means) - there was not a taxable event
2) then you did a Roth conversion from the TRAD IRA to a Roth IRA - this is what the code 7 means - this is the taxable event.
look at line 4b on form 1040 of your tax return. what number is there? it should be whatever is on the Vanguard Form 1099-R in Box 2a. if that is the case, why do you think there is an amendment required?
