Way to fix theTVDB matching directly in the data? which table?

[JuiceWSA]

Do this:

Video File Naming

With LMA in priority, Embedded Titles within MP4/M4V files are preferred - even over a perfect file name. Local Media Assets should - AT ALL TIMES - remain enabled (unless specifically instructed to turn it off). Local Media Assets should be ‘Demoted’, to the bottom of the stack of active agents under ALL tabs in Shows and Movies, but should NOT be disabled. Local Media Assets is needed for many things - it doesn’t need to be given Tip-Top-Priority (as Plex has so hatefully placed it as it’s …

Then refresh metadata.

Your naming/structuring looks good - if you got the right show:
https://thetvdb.com/search?query=hornblower

We hope it’s just the embedded Title Fields (the bogus Title Fields) that are throwing off the match.