Document 1243837.1
I wanted to test the notion that you can simply set a parameter in pfile and spfile and run the Upgrade script again. So, I took a backup, and did just that. The result is this:
ORA-000001: unique constraint violations in SYS.I_STMT_AUDIT_OPTION_MAP and SYS.I_SYSTEM_PRIVILEGE_MAP
I'm not sure if I will get these results when I follow the steps in 1243837.1 on a dtabase with missing x$ tables, but there is the chance. Just thought you might be interested in knowning what happens when you follow the steps and re-run the catupgd.sql script on a database that has no errors.