Howdy from Oklahoma USA to all.
I thought a post might be helpful to some at this point, like me that have been following this thread and working hard to learn and understand how to best use my songbook. Keith has been a very helpful resource as has Rob's posts on the process for utilizing the songbook as it is capable of being used. Don't miss Keith's website on songbook editing and registration.
I now understand how powerful this is. As Keith so clearly discusses, you can almost have an unlimited database that allows you (particularly a performer who plays different styles of gigs and needs different genres of songs), to fully customize different playlists, easily modified either in the songbook function of the Pa2x itself, or in your PC Editor. (You will do both and save each separately in your Editor and back-up your Pa2 from time to time to HD and USB), to include edited styles, sts settings and vocal harmonizer settings. I supppose that once you are happy with the completness of your final songbook, you can erase all others from your Editor and Pa, and just keep a back-up of your completed book. I quickly learned to back-up your existing songbook and custom lists to HD and USB as Keith and Rob suggest, (I did not and had to re-build my custom lists), then begin the merging process (step by step in Keith's tutorial) ,to end up with one songbook that includes all of the bonus ware and other Korg song files, Keith's song project, etc, that we all have acess to through this forum and Keith's site -- or the Korg site.
Please compare your merge results with mine as I end up with 752 edited songs. I have done my best to override the duplicates from the various databases being merged, but I am sure I did not get them all. You have to be careful and not override all songs with the same name as the system asks you if you want to do, as many have the same name but are in fact built with different styles, genres, etc. So, I feel you almost have to merge WITHOUT overriding every song with the same name and wait until you have merged all databases into the one final one, then go through the entire songbook to delete songs that are truely duplicates. This takes some time but is fun, I learned a lot, probably made a mistake or two (or three) along the way but now have a really great resource of songs to build custom lists and perform from. Keith indicates if you merge all appropriate song databases correctly, you should have around 800 fully edited songs. I may have missed a set or two along the way, but I feel I ended up with a very complete songbook for me. Now easily added to later as more become available.
For all Pa2x users, how to save styles to edit(and not lose the factory style set up), and then save as a "song" in your songbook and build "custom lists" is a must to really enjoy and know how to best use this tremendous keyboard. Time well spent guys and gals. Give it a try!!

Oh, and tons of kudos to Keith, Rob, Sharp and the other real experts in this forum who know the Pa2x inside and out, literally.
Judge Bill