There should be no generation loss when copying an ISO 9660 data disc that has higher level error protection and no uncorrectable errors. That is, a data disc with 2,048 bytes of user data per sector. See Mode 1 and Mode 2 Sectors
. Both ISO 9660 Mode 1 and Mode 2 Form 1 discs have an extra 276 bytes of ECC (error correction code) per sector, and should not have copy generation losses when no uncorrectable errors are present.
The conclusion above is the normal condition. However, if a disc containing error correction is read RAW (read byte by byte without applying error correction) and written RAW and copies of copies are made this way, generation errors can be expected. The frequency and severity of errors are dependent on the condition of the original disc, reading accuracy of the reader, and burning accuracy. Discs are usually only read RAW to make a copy of a copy protected disc.
When a disc with no uncorrectable errors is copied, the copy should be checked to make sure that no uncorrectable errors are present. A CRC check may also be done to ensure that the files are 100% accurate.