What looks alike is not necessarily the same. Even so DRAM components of same type and brand look identically there might be some significant differences between them.
Just three decades ago, DRAM memory production was still at its infancy. The price for a single component was a double-digit dollar value. The package, assembly and testing costs accounted only for a very little portion of the total price of the components. Parts that did not pass all the quality expectations during testing were simply scrapped. Since these early times, the scale of economy has forced the memory manufacturers to dramatically reduce the sales-prices and margins by exponentially increasing the output. One key-factor to keep the profitability was to avoid scrapping marginal quality parts. Each and every produced component regardless of the quality level should find a customer that can use it.