re : I can only get results back from the 50 or so messages that haven`t been compacted ?

What does compacting mean in Thunderbird?

When you delete or move emails from a folder eg: Inbox, they appear in another folder or Trash. But the original copy is still in the original folder - in Inbox, but now it is 'marked as deleted' and hidden. So you cannot see them and would not even know they exist, but they are still lurking in that file, bloating it.

When you compact the 'Inbox' folder it removes those hidden marked as deleted emails, so the file actually now only contains what you can see in the list. The size of the mbox file is now smaller because the marked as deleted emails have been erased from that file. The Inbox now has a smaller size and is tidy so less prone to corruption. Compacting a folder is basic housekeeping to help maintain a healthy Thunderbird - it does not delete good wanted emails. It does not empty the Trash. It removes old traces of emails that have already been deleted.

Obviously if email does not exist then it will not be displayed. If email was moved to another folder then it still exists.

If you have an imap account, logon to the webmail account via a browser - do the emails exist on the server? If not on server then they cannot appear in an imap account, as imap accounts can only display whatever is on the server.

I saw you had posted a question earlier this year and set a profile, but looking at the images you posted it was not done properly. For some crazy reason you have got 3 entire complete profile name folders for several profiles inside another profile name folder - no idea how you managed that, it could only have been done manually after creating a profile. Really weird.

It looks like 'Thunderbird-Profile' has been set up as an actual profile name folder and then 3 other profile name folder were moved into it - which is so wrong. I would need to see the contents of the 'profile.ini' file located in the Appdata/Roaming/Thunderbird folder to understand which is which and what you are using.

Do you use a POP or an IMAP account ? It's important because instructions differ depending upon your setup.

When I go on webmail it just has the last 2 wks messages.If I look on outlook on another computer it has 4 years of messages , its the same imap account ! Yes my profile set up maybe a mess.When setting up initially nothing worked when trying to import my old outlook messages .Support dried up , I tried repeatedly and tried different random ways to get them in.Strangely they appeared on my ipad as imported eml files but not in thunderbird however many ways I tried. Basically am i expecting thunderbird to behave like outlook which it can`t ?