Souter never was a district judge -- he was on the Court of Appeals for only a few months.
Clement was a district judge (trial) for about 10 years (appointed by Bush I) and has been a court of appeals Judge for 4 years (longer than Thomas and about the same as Scalia and Bork).
True. He did, however, like Clement spend the bulk of his time prior to being appointed as a trail judge like Clement though he was on the NH Supreme Court for a time before being appointed to the Appeals Court.
The point is, both have/had a thin paper trail.