Using your logic : On April 14 2011 AGO's closing price was $14.05 . On April 15 they settled with BAC for $1.6 billion which equals $8.73 per share using your math the stock should be $22.78. This was a actual settlement not some pie in the sky lawsuit that has no merit. AGO is dirt cheap.
While your arithmetic is accurate, the market doesn't agree with you analysis. Had the market agreed even slightly with your analysis, the share would have sold-off a lot more. One thing is for certain, the $1.4B number is the largest number Lehmann could dream-up. IF the case goes Lehman's way, the amount will be much less. Finally, the market doesn't appear to believe the Lehman suit is much of a threat. Good time to go long here iffin you are not in a big hurry.