For older Communities we know this issue of users creating multiple profiles during their career because often, they might have

• forgotten their usernames and did not know who to contact to regain control,
• or, sometimes they simply did not know that the Admin can update the email address for them

and they can continue to use their existing profiles.

An 'Is This You' check any existing profiles before creating a new one for the User

So just like a realtime password checker, a realtime lookup on the combination of the Name and Last name to suggest profiles in the system that may be of the same person registering.

This certainly is a big cause of duplicate accounts for us and we have offered this manual profile update Service from the center of our homepage on GameChanger, something which is used daily.

A realtime intervention

On the registration form, (thanks to @Alistair FIeld for the screenshot, riffing off it) a search on the User based on their unique Second name or first and second name combination could be used to quickly query the user dB to auto-serve profiles that match to remind the user that they need not dump their existing Community profiles (which they might have not used in a while), just because they changed companies.

This step would significantly reduce users from creating duplicate accounts.