Profile merge/combine and delete??

I guess the safest way to do that would be to import the messages from all those extraneous profiles into local folders in your primary profile. That will still leave you with the task of sifting through them and deciding which ones to keep or not, but at least they'll all be in one place. Once you're satisfied that you have everything you want, you can then delete the old profiles. This process will use a lot of disc space while you're doing it, but when you're done you will reclaim that space.

To do this, use Thunderbird's Import feature...

- I recommend you first make a backup copy of your current profile before starting, just in case something goes wrong. Actually, you should make regular backups anyway if your email is valuable to you. These articles describe Profiles and how to back them up. Use the instructions for manually backing up large profiles - the built-in export tool has some limitations.

https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data

https://support.mozilla.org/en-US/kb/thunderbird-export#w_creating-a-backup-of-large-profiles

- Click on <Tools | Import>, then choose "Import from another Thunderbird installation", then "Continue". You will then be presented with a list of your various other profiles. Chose one and click "Continue".

- De-select everything but "Mail Messages" and click "Continue". You'll see a confirmation window and if that looks good, click "Start Import".

You will wind up with all messages from that old profile in a new Local Folder called "Thunderbird Import"

Now repeat the process for every old profile you wish to merge.

After you eventually have deleted anything you don't want to keep, you can delete any unneeded local folders.

Finally, you can delete the old, obsolete profiles. Easiest way to do that is to go to <Help | Troubleshooting Information | Profiles | about:profiles>. You will find a list of all profiles, each with a "Remove" button.

Is there a way to compare the emails in the older profile to see if they are already in the present profile?

If already there, I can just delete old profile.

I don't think it's possible to automatically compare messages in one profile with those in another.

There are a few add-ons that claim to be able to find duplicate messages within one profile. Search add-ons for "duplicate". I gave this one a quick test drive and it seems to do what it claims.

https://addons.thunderbird.net/en-US/thunderbird/addon/removedupes/

Still takes some time, but better than trying to do it manually