It's possible your mail files are corrupted. First of all create a backup of your Thunderbird profile folder. https://support.mozilla.org/en-US/kb/profiles-tb#w_backing-up-a-profile

Then try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder

Note: depending on the corruption this may erase messages from the affected folder which cannot be recovered anymore. In that case you'd need to restore them from a recent backup done prior to the corruption.

Corruption is often caused by anti-virus software messing with Thunderbird mail files. It is therefore recommended to create an exception for the Thunderbird profile folder, so that the real-time scanner won't attempt to scan the profile with your mail.

For more information on the profile location see http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Also see http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

Thanks for the idea. I did as directed and repaired the folder after creating a backup. Unfortunately it didn't help. The interesting thing is if I use Outlook as the client all of the subject and correspondent data is present.

Are these emails (all your emails in the folder really) still available on web mail?

yes. I tried repairing the folder again. The next time I opened Thunderbird all of the new emails had the subject and correspondents fields filled in. I could not retrospectively fix those that were previously missing but I think the problem is solved going forward. Thanks...