A possibility is that thunderbird could not locate the profile after update if there was any interference, such as from antivirus or VPN. If so, the old profile may still be there. to investigate, do this: - click help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder' - you are now in the profile in windows file explorer, click back one folder so you will be in the 'profiles' folder. - here, if there is another profile, it should be listed. An IMAP account would be in the imapmal folder and a POP account would be in the Mail folder - if it looks right, then, in thunderbird, do this: - click help>troubleshootinginformation - scroll down to 'profiles' and click 'about:profiles' - now, click the 'create profile' button - click next - now, enter a short name for the profile, such as, OLDPROFILE and then click the 'choose' button and locate and select the profile you want, then click finish and launch.

"If you do a search in the c:\users\<yourid>\appdata\roaming\thunderbird\profiles folder, you may find abook.sqlite and history.sqlite. These are the technical filenames of the addresssbook and the collected addressbook. You can import them with tools>import>importfromafile. This sometimes happens, that thunderbird creates a new profile and some content is left behind. No, this does not happen to everyone and is likely a glitch wherein an update was interrupted by another program, such as an antivirus product."

This might help. search for "abook.sqlite". Found it in a file, C:/windows.old. look for last oldest.