So you might feed it your COBOL code and find it only coverts 40%.
I'm afraid you're completely missing my point.
The system gives you a recommendation: that has a 50% chance of being correct.
Let's say the system recommends converting 40% of the code base.
The system converts 40% of the code base. 50% of the converted result is correct.
50% is a random number picked out of thin air. The point is that what you end up with has a good chance of being incorrect and all the problems I mentioned originally apply.