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Step 1 (by Stefan Pohl using the FritzGUI): Filter all games, where (at move 12) both sides still
have a queen and both sides castled to opposite directions.

= 17665 positions (12 moves deep) (out of 397457 games

Working steps 2-5 by Hauke Lutz (PGNscanner: thinking-time/position: 5 seconds (singlecore,
4.5 GHz (i7-4930k, Fritzmark 3367)):

Step 2: Checked database for duplicate games with the PGNscanner. Found nothing (nice work, Adam Hair!)

Step 3: Checked the 12moves-database with Komodo 8 (using PGNscanner (eval-interval of +/-0.50)) and deleted all games with an evaluation outside the eval-interval.

Step 4: Deleted some games of the 12moves-database with ECO-code B and some games with white long castlings for a better balance. Reduced the number of games to 10000. Used EXCEL for this.

Step 5: Mixed the games of the 12moves-database (by hand) by the castling-direction (we didnt want
some thousand games with white long castlings in a row followed by some thousand games with white short