I had to re-install Thunderbird.

Why?

my profile seems to have recreated all my information in the new installation.

Thunderbird separates the program installation and the profile with all your data. Re-installing the application does nothing to your profile.

under archives 2010 there are only two listings, and in 2012, there are none.

http://kb.mozillazine.org/Disappearing_mail

Is there a way to retrieve the many missing ones?

You can always restore things from a backup of your profile folder, assuming you did create one in the first place.

Thank you very much for helping. I delayed my response so that I could be sure that I had tried all suggestions.

(1) I had to re-install Linux Mint after a glitch, so that meant re-installing Thunderbird. Most of my folders are still there, but as I wrote, most of the mail, but not all, that was in Archives by year, has disappeared.

(2) I had already followed the instructions in the link you provided but have gone through them again to see if I missed anything. No joy.

(3) I had felt safe since I have been copying folders to a Transcend Storejet, but I can't find them now.

I have gone to my profile and found that there are three profiles listed (8 characters followed by .default, and none seem to have more than lists I can't comprehend. I realise that I must have done something stupid but wonder what it is.

Any further help will be appreciated.

I'm afraid there isn't much more to suggest based on the information available. You're welcome to ask if you need help restoring stuff from either a backup or an old profile. But then there would need to be something which can be restored in the first place.

Thanks very much for trying.

You did try right clicking, selecting properties and then the repair button. Right?

You did select compact folders from the file menu.

Thank you Matt. I have (had) done those things. When I click on 'repair', nothing happens, but I suppose that means repair is impossible.