You are correct in saying that believers know where they are going at the time of their death. The perfect and complete work of Christ, the eternal validity of the unconditional gospel and the gift of justification through faith alone remain. Any verdict pronounced on Judgment Day will not change the verdict previously pronounced and already known for those who have fallen asleep in Jesus.

But there are many Bible passages that affirm that believers as well as unbelievers will stand before the judgment seat of Christ and will be judged on the Last Day. Among them are these: Matthew 25:31-46, 2 Corinthians 5:10, and Romans 14:10. The basis of the judging will be the gospel, and the verdict issued and known privately at death will not be in jeopardy. Many good purposes for this public judgment may be perceived. This will be a demonstration of divine justice and mercy and affirmation of the believer's gift of saving faith. But this is not to be viewed as a threat to our security centered in Jesus Christ.

Lutheran theologian David Hollaz wrote these comforting and instructive words on this subject:

Question: Whether also the sins of believers will be examined and made public on the day of the Last Judgment?  
Answer: It is not likely that individual sins of believers will on the last day be investigated and specially judged by Christ.  Evidence for this answer:
1) From the divine promise. God has promised to blot out our sins as a cloud (Isaiah 44:22), to cast them behind his back (Isaiah 38:17), to sink them in the depths of the sea (Micah 7:19), that he will no longer remember them (Isaiah 43:25). But what God does not want to remember, he will not publicize.
2) From the immutability of God. His will is unchangeable (Malachi 3:6). And so, since God in this life has forgiven sins to believers, it is unlikely that the same God will recall for rigid examination sins that have been forgiven.
3) From what the Judge has done in the past. Christ will come to judgment as our Redeemer (Luke 21:28). He who presented the church to himself as a glorious church, not having spot or wrinkle or any such thing (Ephesians 5:27), will not bring up the spots of his saints (Examen, pt III, sect II, ch X, qu 13, p 738).