Indeed, the ecommerce system at my company used to use email+password as the account identifier (because reasons) and when we tried to deduplicate we found a lo

Indeed, the ecommerce system at my company used to use email+password as the account identifier (because reasons) and when we tried to deduplicate we found a lot of duplicates were things like SmithFamily@isp.example.com where one account always shipped to "Laura Smith" and the other one always shipped to "Harry Smith".