Yesterday showed I was wrong.
So here is what You should not do at home ;-)
I started with direct setting of compatible parameter to 184.108.40.206.0 (which in turn was a very, very bad move). Because we upgraded quite a bunch of databases I felt quite sure. Another thing was we prepared a procedure for upgrade (based on documents from Metalink, but shortened, as we do not need to go through all the steps) and there the pre-upgrade tool was missing.
So I startup in upgrade mode and after a while I get an error that there is unknown identifier TZ_VERSION in table REGISTRY$DATABASE. The hint in script was simply to run utlu112i.sql - it became clear that there are some changes made by utlu112i.sql to the database structure.
Due to setting compatible parameter to 220.127.116.11.0 I was unable to start this database again as 10g version, so can not run utlu112i.sql. @#$$$%!
Then I tried to add a column to the problematic table. The command was successful, but the structure showed still as old due to running in upgrade mode and apparently in a different edition.
Recreating the controlfiles based on the database structure, which I still was able to query, was successful, but it is not enough because data files were changed as well (probably only headers, but this solution path was thus closed).
What I did finally was a simple ugly hack.
I edited the file $ORACLE_HOME/rdbms/admin/catupstr.sql and changed queries to the REGISTRY$DATABASE replacing TZ_VERSION calls with a value ('14' in my case). Then I just started catupgrd.sql again.
There were some issues with the SI_INFORMATN_SCHEMA schema, but not sure if this has anything to do with problems with pre-upgrade tool and as this is a test environment, it is not so clean as the production (some not compiling code pieces, etc). Eventually the problem was solved.
- do not change compatible parameter to newer when upgrading - do it sometime afterwards
- always run pre-upgrade tool