Preferences and Local State are changed when you change a setting or a flag. Others may change constantly depending on what you do during your surfing time.
Maybe even some extension could be creating those files.
I did it. On my only windows user's account.
To be more precise - initially all my passwords have been working in both Opera versions. Today I decided to stay with version 20 but when I launched the browser it turned out that all my passwords disappeared. I can still use and see them in version 21.
I reinstalled Opera and tried to restore only passwords' files, but I had only version after update. I thought that it could be a problem.
Now I'll try to install Opera 12 again, then upgrade it to version 20 and will see if passwords will start to work. Especially that not only saved passwords vanished but I don't receive any communicates offering me saving new passwords.
What a mess - bigger that my poor English