Data integrity of recorded data products is quantitatively evaluated by enumeration of unreadable, uncorrected, and/or corrected data subsets, and/or by measuring over-sampling of corrected data subsets. Quantitative data integrity evaluation facilitates commerce in pre-owned data products, through pre-owned product re-sellers and/or directly between owners and buyers. Quantitative data integrity evaluation, in conjunction with pre-owned product commerce or performed independently, provides opportunities for gathering product information for data products, including content signature or other unique content-identifying data, for incorporation into product information database(s). Data integrity evaluation, pre-owned data product commerce, and/or data product information gathering may be conducted online. Data integrity evaluation, pre-owned product commerce, and/or data product information gathering may provide opportunities for revenue generation.