Hi, your class 12 paper will be passed through 3 evaluators. The first one will correct your paper, the second evaluator checks whether there are any mistakes in the paper in order to reduce the marks, the third one will recheck the paper. If you get pass marks they don't bother much to correct for the second time. In case you fail the paper might be corrected twice to check if they could add any extra marks to pass. Since Valuations are done in more than one level, it might be some strict. But they don't prefer to fail anymore at max. Hope this clarifies your doubt and brings a smile on your face.

Cheers!!

Good Luck!:)