My experience with tagging IMAP messages in Thunderbird is that those tags will be saved on the server (from what I read they as stored as IMAP keywords), so they are synced, but if you access the same messages with another Thunderbird profile (e.g. from a different computer), you have to re-create the tags in Thunderbird first, and then only will it be able to show those tags on the messages. In other words, you have to tell TB that "those tags exist" or it will not be able to see them.
1/ In the case of a lost Thunderbird profile, which used to contain a lot of tags, is it possible to see all the tags that have been saved to the server, in order to retrieve them? (Either on a per-message basis, or globally)
2/ In the case where the TB profile still exists, is there a way to extract the tags that have been defined in that profile, and then import them to another profile? Or sync them between profiles without having to manually recreate them all?