The data on the bad disk was read without errors apparently. Some programs can be set to retry reading sections that are bad, and this will work on occasion. And trying a poor disk in several drives is also recommended, as drives vary quite a lot in their reading ability.
One of the best programs for reading disks that have deteriorated is called ISOBuster. There is a free version of this program which will work for most types of data. The paid version is slightly more versatile regarding the file systems it will work with.
By the way, the only double layer disks that we recommend using are made by Verbatim.