We are currently on 10.2, but the users were deleted back in 9.1. CS45262 explains how to search for objects created by deleted users. Basically, you set the following property:
xconfmanager -s wt.org.populateUserFullNameFields=true -t codebase/wt.properties -p
The info about the WTUser table behavior is from a recent tech support case dealing with how some (really) old deleted users are being displayed. (Missing first and last name.) Per TS, I will be manually editing those rows in the table to include the currently missing information.