eDiscovery search and how to identify duplicate accounts?

Has anybody faced the following issue:

Company have had an employee whose name was Mary Doe. She was employee e.g. during years 2015 - 2018. Then there was a different Mary Doe employee, and she was in a company during years: 2019 - 2020. This means that both accounts are inactive accounts.

How shall I be able to separate these two accounts when doing content / eDiscovery search? As they both have had the same UPN: mary.doe@company.com, but are both inactive. The GUI at least shows only email address and display name.