They also send some documents to your embassy that verifies if your passport is genuine etc, this is what the SB guy was telling me yesterday as I went there. I am applying citizenship along with my minor children, one of whom is a US citizen, and the SB guy was telling me that he'll prepare letters for the embassy, for them to verify the passport etc. I am assuming I would need to take this sealed letter to the US embassy myself, but as you are saying that the sealed letter includes just the intention of renunciation, which in my minor child , certainly shouldn't be the case.