Thank you for bringing this question to the community! When you upload a contact list, we look for any existing contacts using the same email address. If someone else on the account exists with that same email address, then we simply update the current contact, with any changed information, such as Name, lists, company, Physical address, etc. We do not ever change the 'email address' info on a contact, unless you manually change that, so none of your contacts would have been 'back-dated' to an old email address, though if there were changes to name or company, those might have been reverted to the old data.
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