The transfer is done solely by the OS, so all files, regardless of location within the profile should be copied. The only time that you get a partial copy is when Thunderbird is still running and has not released the files. You can verify the local folders by viewing the profile after having copied it, using Windows File Explorer.

I hear what you are saying but that is not what I am experiencing. I have tried the simple copy paste profile. I have tried the Tools/Import-Export function. I have tried the ImportExport NG add-on. Each option produces it’s own level of failure. Depending on which technique I use it may or may not export all of the mail and may or may not import the mail. After an export or a copy profile I check the mbox files and many show a value of 0 or a value that is less than that same file value before the export. So the mail is lost on export (the program is closed.) With the TB built in Tools/Impoert-Export function it exports the profile to a zip I open to look at it and all mail files look good hardly any mbox with 0 value. I import (the mail only not all the settings) into the new profile and I end up with a flat folder layout (loss of hierarchy) plus new duplicate folders added in with random numbers appended to the folder name plus half the folders are still empty or missing large numbers of emails despite that fact that the mobx files in the zip file were good. When I import using the add-on it imports the top level folders only and nothing more and no email at all despite using the options for folder structure. Just one big mess. This is going on for years. The only way it worked in the past is to use simple copy and paste but it often needs to be done several times before all emails are captured. This one I copied in a few months ago and never checked it and since then added probably somewhere around 50-100 new messages from my imap accounts so I can’t just delete this local folder and reimport using the profile a few months ago I would lose those newly added mail. I also notice that sometimes dragging and dropping a sub folder into another folder all the messages in the folder are gone when it gets to its new location. This is random and so unpredictable that the only way to safely move folders is to create new folders and copy and paste the mail. At this point the only reasonable solution is have someone spend time on this for me and get a conversion of the mbox into EML and put these local files on a windows EML viewer program. TB has been on the market long enough that I would assume moving local mail between profiles should not be a catastrophic event.