Put each list in a database file and create a field in each -- call it identity or something you like, with the same field name in both databases. Fill all records in that field with the same data (maybe the name of the list) but make sure the data in one file is different than the data in hte other file's matching field. Merge the two files into a third (save as separate file).
Most decent databases will let you search for duplicates based on one or more fields, pick the field most relavant, Find all the duplicates, usually there is a command that will invert the search -- in Filemaker Pro it would be "show ommitted". Those records will be the extra records and will be identified which original database they came from by the data you put in the field you created at the start.
Export, sort, do whatever you like, as the British say: Bob's your uncle".
Edited by 1916Luger, 12 June 2013 - 08:16 PM.