A sortie is defined as one pilot takeoff (launch) followed by one flight termination (shotdown, landed, ditched, bailed, disco). You can get multiple sorties even in one life events when pilots are allowed to bail/replane at the start or disco/replane with CM permission.
There were 3 B-29 events: 2012-12, 2013-12, and 2014-10 with 3 frames each. I just did a quick scan of the html files and you are correct. There were only 318 sortie departures listed. I just validated that the DB has 318 sorties, so now I need to go back and find what I did wrong with a SQL JOIN.
The stats are skewed by the bomb and bailers who have no intention of getting back home.
By the way, I show plissken as the CM for all three frames for Operation Clarion, though perhaps it was multiple people and plissken just happened to be the one dealing with the logs?