Who sent you the new profile? Did you have a previous profile? You have not provided enough information to advise.

The update request came from Thunderbird mail. So when the updated version was installed it wiped out hundreds of emails. I would like to recover them. The update notice said this won't happen.

It may be that Thunderbird lost the profile. Is the account still there, or did Thunderbird prompt to create an account? If it prompted, my suggestion is to ignore the prompt, click the Home tab, and - if menu bar isn't showing, then right-click, select Menu bar, and then click help>moretroubleshooting information, scroll down to Profiles, click 'about:profiles' and then browse that next panel to see if your account is there.