In this tutorial I'll walk you through several images, some as many as three stops overexposed and some almost 2 stops underexposed and show you what I discovered. I will tell you that the ones that were three stops overexposed, even those that were two stops overexposed cannot be saved. That was also true with the duplicate RAW files I also use this comparison in my demonstration.
Understand that my exposures are pretty consistent throughout an entire event. The images I chose to use were just a few image hic-cups every photographer experiences in the course of a nine hour shoot. But what was most surprising to me was the fact that I could easily recover data from JPEG files that were 1 - 1 1/2 stops overexposed and 1 - 1 1/2 stops underexposed! The LR4 adjusted images looked quite good!